Mathys Ltd., Switzerland supports the funding of the clinical and radiological multicenter study.

The presented research has been performed in compliance with all institutional, national, and international guidelines for human welfare. Institutional review board approval has been obtained.
<ol>
	<li>Position the patient in supine position on a standard operating table with two separate leg supports. Allow the ipsilateral legs to remain mobile.</li>
	<li>Apply standard sterile coverage suitable for the antero-lateral approach in supine position.</li>
	<li>Slightly flex the ipsilateral side using a knee roll. In addition, hyperextend the contralateral side about 15&#176; for the femoral preparation.</li>
	<li>Locate the tip of the greater trochanter as well as the anterior superior iliac spine by palpation serving as orientation.</li>
	<li>Perform the skin- incision using a surgical knife (6 - 12 cm, depending on the patient&#39;s anatomy) centered on the tip of the greater trochanter aiming at the anterior superior iliac spine above the intermuscular septum between the gluteus medius and the tensor fasciae latae.</li>
	<li>After incision of subcutaneous fat, use two skin retractors anteriorly and posteriorly. Open the fascia without causing damage to the tensor fasciae latae.</li>
	<li>Do a blunt dissection using your index finger, pushing the gluteal muscles posteriorly without damage.</li>
	<li>Expose the joint capsule using three retractors.</li>
	<li>Perform the capsulectomy alongside the femoral neck. 
	NOTE: No sharp dissection of any muscle, in particular the gluteal muscles, is needed.</li>
	<li>After removal of the anterior joint capsule, expose the femoral neck in order to perform the osteotomy by placing the two facing curved retractors intracapsular around the femoral neck (Figure 1). 
	NOTE: The most important step in the implantation of a calcar-guided short stem is the choice of the individual level of the osteotomy. This way, stem-positioning can be done individually in a great variety, resulting in a large bandwidth of CCD-angles to be reconstructed (Figure 2; Figure 3). Consequently, a preoperative planning is mandatory to display the exact level (Figure 4: red line (OL: level of osteotomy)).</li>
	<li>For the surgeon&#39;s orientation, in order to determine the level of the osteotomy, perform a palpation of the lesser trochanter and the fossa piriformis. If a valgus position is desired according to the preexisting anatomy, perform the osteotomy distally by resecting most of the femoral neck (Figure 5a). In order to align the stem in a varus position, resect proximally, retaining most of the femoral neck, according to the preoperative planning (Figure 5c). Femoral offset and leg length can thus be maintained precisely (Figure 5).</li>
	<li>Perform the osteotomy (Figure 1) in slight external rotation of the ipsilateral leg according to the preoperative planning using a long stiff bladed oscillating saw.</li>
	<li>Remove the femoral head from the acetabulum using the femoral head extractor. To protect the gluteus medius, place a &#34;Langenbeck&#34;-retractor medially and pull proximally.</li>
	<li>During acetabular preparation, insert a &#34;Steinmann&#34;-pin in the proximal end of the acetabulum to protect the gluteal muscles.</li>
	<li>Expose the acetabulum using two extractors.</li>
	<li>Implant the acetabular component according to the preoperative planning and depending on the patient&#39;s individual anatomy.</li>
	<li>For femoral preparation, first remove the knee roll and hyperextend the contralateral leg about 15&#176;. Now perform a 90&#176; external rotation and a maximum of 90&#176; flexion of the knee joint. Have the assistant hold the subject&#39;s leg at maximal adduction (about 40&#176;).</li>
	<li>Position two retractors on the medial side of the proximal femoral neck and proximally at the posterior (medial) cortical end of the femoral neck. Avoid contact to the greater trochanter, to minimize the risk of possible damage to the bone and the muscle insertions.</li>
	<li>Apply the &#34;round-the-corner&#34; technique to open the proximal femur alongside the calcar with the curved opening awl. 
	NOTE: Posterior structures such as the greater trochanter or the gluteal muscles are not affected.</li>
	<li>Drive in gently specially curved, implant-shaped rasps in ascending sizes using a hammer in order to prepare the proximal femur and the femoral canal until cortical contact and a stable fit and fill are reached. Note that a double offset minimally-invasive rasp handle is available. Perform the insertion guided by the calcar in the &#34;round-the-corner&#34; technique (Figure 6).</li>
	<li>Choose one of the two available trial cones with different offset versions (standard and lateral offset) according to the preoperative planning.</li>
	<li>Assess an intraoperative fluoroscopy using a digital image intensifier after inserting a trial head and performing a trial reduction to compare the positioning of the rasp (trial implant) to the preoperative planning (Figure 7). Perform an anterior-posterior radiograph. To screen the second plane, also perform an axial view radiograph. Perform adjustments, if necessary. 
	NOTE: Reaching cortical contact is essential regarding the risk of postoperative subsidence. Avoid undersizing! (Figure 8)</li>
	<li>Remove the trial implants and insert the definitive implant containing the chosen offset version using the special implant impactor. Note that the original stem aligns itself exactly like the trial rasp (Figure 9).</li>
	<li>After the final reduction by applying axial tension combined with internal rotation of the leg, complete the procedure by standard wound closure.</li>
	<li>In most cases, allow full weight-bearing after surgery using 2 crutches under physiotherapeutic surveillance starting 4 h after the operation. 
	NOTE: In heavy patients, primary stability might be impaired, thus, weight bearing protocol must be adjusted accordingly.</li>
	<li>Provide analgesics according to the intensity of pain recorded, non-steroidal-anti-inflammatory-drugs (NSAID) to prevent heterotopic ossification, and venous thromboembolic prophylaxis.</li>
</ol>

<ol>
	<li>Jerosch, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Kurzschaftendoprothesen an der H&#252;fte. , (2017).</li><li>Kutzner, K. P., Donner, S., Schneider, M., Pfeil, J., Rehbein, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=One-stage+bilateral+implantation+of+a+calcar-guided+short-stem+in+total+hip+arthroplasty.">One-stage bilateral implantation of a calcar-guided short-stem in total hip arthroplasty.</a> Oper Orthop Traumatol. , (2017).</li><li>Anderl, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=2-Jahres-Ergebnisse+mit+dem+Optimys-Kurzschaft+über+den+direkten+anterolateralen+Zugang.+JATROS.">2-Jahres-Ergebnisse mit dem Optimys-Kurzschaft über den direkten anterolateralen Zugang. JATROS.</a> Orthop&#228;die &amp; Rheumatologie 05/2015. 05, (2015).</li><li>Kutzner, K. P., Kovacevic, M. P., Roeder, C., Rehbein, P., Pfeil, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reconstruction+of+femoro-acetabular+offsets+using+a+short-stem.">Reconstruction of femoro-acetabular offsets using a short-stem.</a> Int Orthop. 39 (7), 1269-1275 (2015).</li><li>Matsushita, A., Nakashima, Y., Jingushi, S., Yamamoto, T., Kuraoka, A., Iwamoto, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+the+Femoral+Offset+and+the+Head+Size+on+the+Safe+Range+of+Motion+in+Total+Hip+Arthroplasty.">Effects of the Femoral Offset and the Head Size on the Safe Range of Motion in Total Hip Arthroplasty.</a> J Arthroplasty. 24, 646-651 (2009).</li><li>Asayama, I., Chamnongkich, S., Simpson, K. J., Kinsey, T. L., Mahoney, O. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reconstructed+hip+joint+position+and+abductor+muscle+strength+after+total+hip+arthroplasty.">Reconstructed hip joint position and abductor muscle strength after total hip arthroplasty.</a> J Arthroplasty. 20, 414-420 (2005).</li><li>Kutzner, K. P., Pfeil, J., Kovacevic, M. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preoperative+digital+planning+versus+postoperative+outcomes+in+total+hip+arthroplasty+using+a+calcar-guided+short+stem:+frequent+valgization+can+be+avoided.">Preoperative digital planning versus postoperative outcomes in total hip arthroplasty using a calcar-guided short stem: frequent valgization can be avoided.</a> Eur J Orthop Surg Traumatol. 27 (5), 643-651 (2017).</li><li>H&#246;hle, P., Schr&#246;der, S. M., Pfeil, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+between+preoperative+digital+planning+and+postoperative+outcomes+in+197+hip+endoprosthesis+cases+using+short+stem+prostheses.">Comparison between preoperative digital planning and postoperative outcomes in 197 hip endoprosthesis cases using short stem prostheses.</a> Clin Biomech. 30 (1), 46-52 (2015).</li><li>Kutzner, K. P., Freitag, T., Donner, S., Kovacevic, M. P., Bieger, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Outcome+of+extensive+varus+and+valgus+stem+alignment+in+short-stem+THA:+clinical+and+radiological+analysis+using+EBRA-FCA.">Outcome of extensive varus and valgus stem alignment in short-stem THA: clinical and radiological analysis using EBRA-FCA.</a> Arch Orthop Trauma Surg. (3), 431-439 (2016).</li><li>Kutzner, K. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Incidence+of+heterotopic+ossification+in+minimally+invasive+short-stem+THA+using+the+modified+anterolateral+approach.">Incidence of heterotopic ossification in minimally invasive short-stem THA using the modified anterolateral approach.</a> Hip Int. , (2017).</li><li>Kutzner, K. P., Kovacevic, M. P., Roeder, C., Rehbein, P., Pfeil, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reconstruction+of+femoro-acetabular+offsets+using+a+short-stem.">Reconstruction of femoro-acetabular offsets using a short-stem.</a> Int Orthop. , (2014).</li><li>Kutzner, K. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=One-stage+bilateral+versus+unilateral+short-stem+total+hip+arthroplasty:+comparison+of+migration+patterns+using+"Ein-Bild-Roentgen-Analysis+Femoral-Component-Analysis".">One-stage bilateral versus unilateral short-stem total hip arthroplasty: comparison of migration patterns using "Ein-Bild-Roentgen-Analysis Femoral-Component-Analysis".</a> Int Orthop. 41 (1), 61-66 (2017).</li><li>Kutzner, K. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Radiographic+alterations+in+short-stem+total+hip+arthroplasty:+a+2-year+follow-up+study+of+216+cases.">Radiographic alterations in short-stem total hip arthroplasty: a 2-year follow-up study of 216 cases.</a> Hip Int. 26 (3), 278-283 (2016).</li><li>Kutzner, K. P., Kovacevic, M. P., Freitag, T., Fuchs, A., Reichel, H., Bieger, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+patient-related+characteristics+on+early+migration+in+calcar-guided+short-stem+total+hip+arthroplasty:+a+2-year+migration+analysis+using+EBRA-FCA.">Influence of patient-related characteristics on early migration in calcar-guided short-stem total hip arthroplasty: a 2-year migration analysis using EBRA-FCA.</a> J Orthop Surg Res. 11 (1), 29 (2016).</li><li>Kovacevic, M. P., Pfeil, J., Kutzner, K. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Implantation+of+a+new+short+stem+in+simultaneous+bilateral+hip+arthroplasty+-+a+prospective+study+on+clinical+and+radiographic+data+of+54+consecutive+patients.">Implantation of a new short stem in simultaneous bilateral hip arthroplasty - a prospective study on clinical and radiographic data of 54 consecutive patients.</a> OUP. 10, 456-461 (2014).</li><li>Hochreiter, J., Hejkrlik, W., Emmanuel, K., Hitzl, W., Ortmaier, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Blood+loss+and+transfusion+rate+in+short+stem+hip+arthroplasty.+A+comparative+study.">Blood loss and transfusion rate in short stem hip arthroplasty. A comparative study.</a> Int Orthop. , 1-7 (2016).</li><li>Bieger, R., Ignatius, A., Decking, R., Claes, L., Reichel, H., D&#252;rselen, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Primary+stability+and+strain+distribution+of+cementless+hip+stems+as+a+function+of+implant+design.">Primary stability and strain distribution of cementless hip stems as a function of implant design.</a> Clin Biomech. 27 (2), 158-164 (2012).</li><li>Loweg, L., Kutzner, K. P., Rehbein, P., Stephan, H., Pfeil, J., Schneider, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wertigkeit+der+intraoperativen+R&#246;ntgenkontrolle+in+der+prim&#228;ren+H&#252;ftendoprothetik.">Wertigkeit der intraoperativen R&#246;ntgenkontrolle in der prim&#228;ren H&#252;ftendoprothetik.</a> OUP. 5 (6), 334-338 (2016).</li></ol>

J. Pfeil is a medical advisor for Mathys Ltd., Switzerland.

Calcar-guided short stems provide many advantages in modern THA compared to conventional straight-stem designs in short-term follow-up. However, only a few results are published regarding mid- and long-term follow-up.
Due to the short and curved design of calcar-guided short stems, the soft-tissue sparing implantation appears to be technically easy. However, the individualized implantation technique requires distinct knowledge about the characteristics of different varus- and valgus positioning. A severe learning curve must be taken into account.
Modifications and Troubleshooting:
Given the individualized positioning of calcar-guided short stems, the preparation of a preoperative planning is absolutely mandatory8 (Figure 4). Besides the detection of the correct implant sizes, especially the alignment of the stem along with the desired level of the osteotomy can be determined. Intraoperatively, using the inserted trial rasp, after reduction of the hip a comparison to the preoperative planning can be done by performing intraoperative fluoroscopy19 (Figure 7). The lateral shoulder of the implant serves as orientation regarding leg length.
Limitations of the Technique:
Investigations suggest a broad bandwidth of different hip anatomies to be adequately reconstructed using calcar-guided short stems5,8 (Figure 2; Figure 3). Previous studies have investigated the outcome of extensive varus- and valgus stem alignment10. After 2 years no revision surgery was needed and the rate of radiographic alterations indicating abnormal stress distribution in total was low. However, especially for valgus-hips a pronounced initial subsidence was observed10.
Particularly for young and unexperienced surgeons the presented technique may come with undesired pitfalls.
Significance with Respect to Existing Methods:
The implantation technique of calcar-guided short stems with individualized neck resection differs from conventional straight stems and certain neck resecting and neck retaining short-stems. Conventional straight stems provide diaphyseal anchorage along with a mostly standardized level of osteotomy of the femoral neck. The preexisting hip anatomy can only be reconstructed by using different offset-versions of the implant5. In extensive varus anatomies for example, this often cannot be achieved properly (Figure 10). Valgization has been found to be the limiting factor in the successful reconstruction of hip geometry also in many previous short-stem designs, causing reduced offset and increased leg length9.
Critical Steps Within the Protocol:
The most critical step consists of choosing the right level of the osteotomy. Furthermore, in order to intraoperatively correctly realize the preoperative planning, a verification using fluoroscopy is needed.
Given a shortening of stem length in calcar-guided short-stem THA, primary stability potentially causes concerns18. The predominant type of fixation is metaphyseal anchoring, based on the fit-and-fill principle. However, due to the option of individualized positioning of these stem-designs, the type of anchoring might differ distinctly. In varus alignment three-point anchoring is common with cortical contact to the lateral cortex of the partially resected neck, the medial calcar, and the lateral cortex at the tip of the stem. However, depending on positioning and sizing, especially in extensive valgus alignment, pronounced diaphyseal anchorage is possible10. In those cases, a securely achieved cortical contact to the distal lateral cortex, as well as to the distal medial cortex is crucial. In valgus position a missing cortical contact of the tip has been frequently observed in the early collective including the learning curve, particularly in cases of undersizing. Therefore, surgeons should take into account, that particularly in valgus hips, undersizing accompanied with a lack of contact to the lateral cortex, might cause initial instability and subsequent implant micromovement10. The usage of intraoperative fluoroscopy to identify undersizing of the stem is therefore highly recommended19.
The present description of the technique, regarding reconstruction of offset, refers only to a two-dimensional analysis. However, given a partially retained femoral neck, short stems will position themselves almost automatically along the anteversion and anterior tilt of the preexisting proximal femoral bone. In particular in varus-hips, this leads to distinct anterior tilting in the axial plane with the stem&#39;s tip being positioned anteriorly (Figure 11). Thus, anterior offset can be reconstructed as well. Further monitoring of this new generation of short stems and the implantation technique in mid- and long-term follow-up is mandatory.

Modern calcar-guided short-stems have been increasingly used in THA in recent years1. New calcar-guided, metaphyseal anchoring short-stems are emerging that focus on sparing muscles, soft-tissue, and bone2,3, thus allowing minimally-invasive (MIS) techniques and approaches to be successfully applied4.
The possible benefits of calcar-guided short-stem THA can be accomplished through a special implantation technique, which differs from conventional techniques used with traditional straight-stem designs. The most important aspect, in this regard, is the anatomical curvature, which has been adapted from the calcar. The positioning of the stem follows the individual anatomy alongside the calcar curve, and permits individualized implantation5. Applying the so called &#34;round-the-corner&#34; technique, the greater trochanter region and most importantly the gluteal muscles, can be spared almost completely2.
Modern THA is largely dependent on the successful preservation of hip geometry. The accurate reconstruction of the hip joint anatomy is crucial for the clinical outcome. The femoro-acetabular offset has increasingly come into focus5. Reduced offset might lead to gluteal insufficiency along with instability of the hip joint and increased risk of dislocation6,7. On the other hand, a severe increase in offset can cause trochanteric bursitis. Given these findings, it appears that undesired changes of offset have great clinical relevance.
Reconstruction of the femoral offset is highly dependent on the ability to reproduce different CCD-angles8. However, valgization has been found to be the limiting factor in the successful reconstruction of hip geometry in many stem designs, causing reduced offset and increased leg length9. The reconstruction of different CCD-angles, in this regard, seems to be the key to accomplish the retainment of the hip anatomy.
In calcar-guided short-stem THA, stem alignment can be individualized, which supports the successful reconstruction of the femoral offset8. Guiding the stem alongside the calcar, the positioning of the stem in the proximal femur is dependent on the resection level of the femoral neck. Given a preexisting varus anatomy, a high resection also results in a varus position of the implant, maintaining a large femoral offset. On the other hand, given a preexisting valgus anatomy, a low resection results in a valgus position, causing a small femoral offset10 (Figure 1; Figure 2).
Consequently, the presented individualized implantation technique allows a broad reconstruction of CCD-angles and thus enables a precise preservation of hip geometry. The presented technique differs from conventional total hip arthroplasty and potentially includes a severe learning curve.

<table><tbody><tr><td>optimys short stem</td><td>Mathys Ltd., Switzerland</td><td></td><td>Implant</td></tr></tbody></table>

individualized stem-positioning in calcar-guided short-stem total hip arthroplasty

Bone- and soft-tissue sparing short stems are increasingly used in total hip arthroplasty (THA). However, there are a large variety of models of short stems, differing in design and function. Calcar-guided short stems provide an anatomical curvature in the medial calcar region, thus, positioning is done individually alongside the calcar in the "round-the-corner" technique. Depending on the level of the neck's osteotomy, stems can be aligned individually in a large bandwidth of varus- and valgus anatomies. This differs from conventional total hip arthroplasty and potentially includes a severe learning curve. Given that a great variety of caput-collum-diaphyseal (CCD)-angles can be retained, the reconstruction of femoro-acetabular offsets can be achieved precisely. However, particularly extensive varus- and valgus positioning has raised concerns in regard to stability and bone remodeling. The purpose of the present manuscript is to showcase the implantation technique in calcar-guided short-stem THA and to summarize short-term clinical and radiological results.

Several short-term results of the investigated short-stem have previously been published, mostly arising from an ongoing observational study at the author's institution2,8,11,12,13,14,15,16. Using the presented technique, the reconstruction of different femoro-acetabular offsets can be accomplished precisely5. Particularly the ability to preserve the preexisting CCD-angle allows physiological hip geometry retainment8. After two years, only a few radiological alterations, such as stress-shielding and cortical hypertrophy were obvious14. The minimally-invasive technique caused low incidences of heterotopic ossifications11. Therefore, the blood loss and transfusion rate remains at a lower rate compared to the implantation technique using conventional straight stems17.
Excellent clinical results have led to successful usage of this technique in one-stage bilateral short-stem THA2. Ein-Bild-Roentgen-Analyses "femoral component analysis" (EBRA-FCA) of the presented implant have shown an increased initial axial subsidence especially in heavy and active male patients, given full weight bearing postoperatively, however, without any clinical consequences in the early stage13,15. Particularly stems that have been aligned in the valgus position result in increased early subsidence, but undersizing and insufficient cortical contact laterally, could be identified as the main cause18.
<img alt="Surgical incision diagram showing retractors and abdominal anatomy during hernia repair procedure." class="xfigimg" src="/files/ftp_upload/56905/56905fig1.jpg" data-altupdatedat="1747911167000" data-alt="Figure 1"> 
Figure 1: Osteotomy of the femoral neck. The osteotomy is done according to the preoperative planning. The level of the osteotomy is determined by palpating the lesser trochanter and the tip of the greater trochanter, serving as a reference. From2,4.
<img alt="Hip joint replacement X-ray showing artificial hip implant." class="xfigimg" src="/files/ftp_upload/56905/56905fig2.jpg" data-altupdatedat="1747911167000" data-alt="Figure 2"> 
Figure 2: Valgus positioning. The stem is aligned in valgus position following a low osteotomy.
<img alt="Hip replacement X-ray showing prosthesis placement and alignment; orthopedic medical imaging." class="xfigimg" src="/files/ftp_upload/56905/56905fig3.jpg" data-altupdatedat="1747911167000" data-alt="Figure 3"> 
Figure 3: Varus positioning. The stem is aligned in varus position following a high osteotomy.
<img alt="Hip joint biomechanics diagram; femur stress analysis showing mechanical vectors and angles." class="xfigimg" src="/files/ftp_upload/56905/56905fig4.jpg" data-altupdatedat="1747911167000" data-alt="Figure 4"> 
Figure 4: Preoperative planning. Blue: Template of the calcar-guided short stem; red: template of the cement-less cup. The level of osteotomy is determined according to the preoperative planning (OL). Intraoperatively, also the height of the lateral shoulder of the implant serves as orientation (SH). Most importantly the stem has to be upsized until cortical contact laterally is reached (CC).
<img alt="Hip joint prosthesis diagram; comparative implant angles and alignment; orthopedic illustration." class="xfigimg" src="/files/ftp_upload/56905/56905fig5.jpg" data-altupdatedat="1747911167000" data-alt="Figure 5"> 
Figure 5: Individualized level of osteotomy and stem alignment. The positioning of the stem in the proximal femur is dependent on the resection level of the femoral neck. Given a varus anatomy, a high resection also results in a varus position of the implant, maintaining a large femoral offset (c). On the other hand, given a valgus anatomy, a low resection results in a valgus position, causing a small femoral offset (a).10,12 From Kutzner et al.2 <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56905/56905fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Surgical incision procedure, showing retractors, muscle layers; orthopedic method, detailed anatomy illustration." class="xfigimg" src="/files/ftp_upload/56905/56905fig6.jpg" data-altupdatedat="1747911167000" data-alt="Figure 6"> 
Figure 6: Round-the-corner technique. The insertion is done alongside the medial calcar, not affecting lateral structures. Especially the greater trochanter and the gluteal muscles can be spared. From Kutzner et al.2 <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56905/56905fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Fluoroscopy setup displaying bone imaging results; X-ray analysis, medical imaging equipment." class="xfigimg" src="/files/ftp_upload/56905/56905fig7.jpg" data-altupdatedat="1747911167000" data-alt="Figure 7"> 
Figure 7: Intraoperative fluoroscopy. After completing trial reduction, the assessment of intraoperative radiography in two planes using a digital image intensifier should be considered mandatory to be able to compare the positioning of the rasp (trial implant) to the preoperative planning. Potential adjustments can be performed subsequently. From Kutzner et al.2 <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56905/56905fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Hip replacement X-ray; medical imagery; orthopedic implant; left and right side comparison." class="xfigimg" src="/files/ftp_upload/56905/56905fig8v2.jpg" data-altupdatedat="1747911167000" data-alt="Figure 8"> 
Figure 8: Example of undersizing. Insufficient cortical contact and undersizing (a) results in subsequent subsidence in the 2 year follow-up (b). <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56905/56905fig8v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Surgical procedure diagram; hip replacement setup showing retractors and incision site." class="xfigimg" src="/files/ftp_upload/56905/56905fig9v2.jpg" data-altupdatedat="1747911167000" data-alt="Figure 9"> 
Figure 9: Implantation of the original calcar-guided short stem. The original implant positions itself exactly like the trial rasp. From Kutzner et al.2
<img alt="Hip joint prosthesis alignment; X-ray diagram showing implant positioning and static equilibrium analysis." class="xfigimg" src="/files/ftp_upload/56905/56905fig10v2.jpg" data-altupdatedat="1747911167000" data-alt="Figure 10"> 
Figure 10: Examples of offset-reconstruction in varus-hips with different stem types. (a, b) Offset-reconstruction cannot be achieved due to diaphyseal anchorage and design of conventional straight stems. (c) Varus-alignment with a calcar-guided short stem accomplishes an exact reconstruction of offset. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56905/56905fig10v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Hip replacement X-ray, comparison of prosthetic alignment, medical imaging, postoperative evaluation." class="xfigimg" src="/files/ftp_upload/56905/56905fig11.jpg" data-altupdatedat="1747911167000" data-alt="Figure 11"> 
Figure 11: Example of the intraoperative fluoroscopy in two planes. (a) a.p. view; (b) axial view. Short stems will position themselves almost automatically along the anteversion and anterior tilt of the preexisting proximal femoral bone. Thus, anterior offset can also be restored. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56905/56905fig11large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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Individualized Stem-positioning in Calcar-guided Short-stem Total Hip Arthroplasty

This protocol describes the round-the-corner technique and the individualized stem-positioning of calcar-guided short stems alongside the medial calcar, depending on the level of the osteotomy. This differs from conventional total hip arthroplasty and includes a learning curve.

Bone- and soft-tissue sparing short stems are increasingly used in total hip arthroplasty (THA). However, there are a large variety of models of short ...

individualized-stem-positioning-calcar-guided-short-stem-total-hip

Nanyang Technological University

Research

JoVE Journal

Medicine

11.7K Views.  St. Josefs Hospital Wiesbaden. Dit protocol beschrijft de ronde-de-HoekKader techniek en de geïndividualiseerde stam-positionering van calcar-geleide korte stengels naast de mediale calcar, afhankelijk van het niveau van de osteotomie. Dit verschilt van de conventionele totale heup artroplastiek en omvat een het leren kromme.

Video: Individualized Stem-positioning in Calcar-guided Short-stem Total Hip Arthroplasty

Use of Human Perivascular Stem Cells for Bone Regeneration

Human perivascular stem cells (PSCs) can be isolated in sufficient numbers from multiple tissues for purposes of skeletal tissue engineering1-3. PSCs are a FACS-sorted population of 'pericytes' (CD146+CD34-CD45-) and 'adventitial cells' (CD146-CD34+CD45-), each of which we have previously reported to have properties of mesenchymal stem cells. PSCs, like MSCs, are able to undergo osteogenic differentiation, as well as secrete pro-osteogenic cytokines1,2. In the present protocol, we demonstrate the osteogenicity of PSCs in several animal models including a muscle pouch implantation in SCID (severe combined immunodeficient) mice, a SCID mouse calvarial defect and a femoral segmental defect (FSD) in athymic rats. The thigh muscle pouch model is used to assess ectopic bone formation. Calvarial defects are centered on the parietal bone and are standardly 4 mm in diameter (critically sized)8. FSDs are bicortical and are stabilized with a polyethylene bar and K-wires4. The FSD described is also a critical size defect, which does not significantly heal on its own4. In contrast, if stem cells or growth factors are added to the defect site, significant bone regeneration can be appreciated. The overall goal of PSC xenografting is to demonstrate the osteogenic capability of this cell type in both ectopic and orthotopic bone regeneration models.

Human perivascular stem cells (PSCs) are a novel stem cell class for skeletal tissue regeneration similar to mesenchymal stem cells (MSCs). PSCs can be isolated by FACS (fluorescence activated cell sorting) from adipose tissue procured during standard liposuction procedures, then combined with an osteoinductive scaffold to achieve bone formation in vivo.

Human perivascular stem cells (PSCs) can be isolated in sufficient numbers from multiple tissues for purposes of skeletal tissue engineering1-3. PSCs are ...

Bioengineering

A Teleoperated Robotic System-Assisted Percutaneous Transiliac-Transsacral Screw Fixation Technique

Transiliac-transsacral screw fixation is challenging in clinical practice as the screws need to break through six layers of cortical bone. Transiliac-transsacral screws provide a longer lever arm to withstand the perpendicular vertical shear forces. However, the screw channel is so long that a minor discrepancy can lead to iatrogenic neurovascular injuries. The development of medical robots has improved the precision of surgery. The present protocol describes how to use a new teleoperated robotic system to execute transiliac-transacral screw fixation. The Robot was operated remotely to position the entry point and adjust the orientation of the sleeve. The screw positions were evaluated using postoperative computed tomography (CT). All the screws were safely implanted, as confirmed using intraoperative fluoroscopy. Postoperative CT confirmed that all the screws were in the cancellous bone. This system combines the doctor's initiative with the Robot's stability. The remote control of this procedure is possible. Robot-assisted surgery has a higher position-retention capacity compared with conventional methods. In contrast to active robotic systems, surgeons have full control over the operation. The robot system is fully compatible with operating room systems and does not require additional equipment.

Teleoperated robotic system-assisted percutaneous transiliac-transsacral screw fixation is a feasible technique. Screw channels can be implemented with high accuracy owing to the excellent freedom of movement and stability of the robotic arms.

Transiliac-transsacral screw fixation is challenging in clinical practice as the screws need to break through six layers of cortical bone. ...

Engineering

Cone Beam Intraoperative Computed Tomography-based Image Guidance for Minimally Invasive Transforaminal Interbody Fusion

Transforaminal lumbar interbody fusion (TLIF) is commonly used for the treatment of spinal stenosis, degenerative disc disease, and spondylolisthesis. Minimally invasive surgery (MIS) approaches have been applied to this technique with an associated decrease in estimated blood loss (EBL), length of hospital stay, and infection rates, while preserving outcomes with traditional open surgery. Previous MIS TLIF techniques involve significant fluoroscopy that subjects the patient, surgeon, and operating room staff to non-trivial levels of radiation exposure, particularly for complex multi-level procedures. We present a technique that utilizes an intraoperative computed tomography (CT) scan to aid in placement of pedicle screws, followed by traditional fluoroscopy for confirmation of cage placement. Patients are positioned in the standard fashion and a reference arc is placed in the posterior superior iliac spine (PSIS) followed by intraoperative CT scan. This allows for image-guidance-based placement of pedicle screws through a one-inch skin incision on each side. Unlike traditional MIS-TLIF that requires significant fluoroscopic imaging during this stage, the operation can now be performed without any additional radiation exposure to the patient or operating room staff. After completion of the facetectomy and discectomy, final TLIF cage placement is confirmed with fluoroscopy. This technique has the potential to decrease operative time and minimize total radiation exposure.

The purpose of this article is to provide image-guidance for minimally invasive transforaminal interbody fusion.

Transforaminal lumbar interbody fusion (TLIF) is commonly used for the treatment of spinal stenosis, degenerative disc disease, and spondylolisthesis. ...

C-arm-Free Simultaneous OLIF51 and Percutaneous Pedicle Screw Fixation in a Single Lateral Position

Oblique lumbar interbody fusion (OLIF) is an established technique for the indirect decompression of lumbar canal stenosis. However, OLIF at the L5-S1 level (OLIF51) is technically difficult because of the anatomical structures. We present a novel simultaneous technique of OLIF51 with percutaneous pedicle screw fixation without fluoroscopy. The patient is placed in a right lateral decubitus position. A percutaneous reference pin is inserted into the right sacroiliac joint. An O-arm scan is performed, and 3D reconstructed images are transmitted to the spinal navigation system. A 4 cm oblique skin incision is made under navigation guidance along the pelvis. The internal/external and transverse abdominal muscles are divided along the muscle fibers, protecting the iliohypogastric and ilioinguinal nerves. Using a retroperitoneal approach, the left common iliac vessels are identified. Special muscle retractors with illumination are used to expose the L5-S1 intervertebral disc. After disc preparation with navigated instruments, the disc space is distracted with navigated trials. Autogenous bone and demineralized bone material are then inserted into the cage hole. The OLIF51 cage is inserted into the disc space with the help of a mallet. Simultaneously, percutaneous pedicle screws are inserted by another surgeon without changing the lateral decubitus position of the patient.
In conclusion, C-arm-free OLIF51 and simultaneous percutaneous pedicle screw fixation are performed in a lateral position under navigation guidance. This novel technique reduces surgical time and radiation hazards.

C-arm-free oblique lumbar interbody fusion at the L5-S1 level (OLIF51) and simultaneous pedicle screw fixation are performed in a lateral position under navigation guidance. This technique does not expose the surgeon or operating staff to radiation hazards.

Oblique lumbar interbody fusion (OLIF) is an established technique for the indirect decompression of lumbar canal stenosis. However, OLIF at the L5-S1 ...

The Use of Mixed Reality in Custom-Made Revision Hip Arthroplasty: A First Case Report

The technology of 3D printing and visualization of anatomical structures is rapidly growing in various fields of medicine. A custom-made implant and mixed reality were used to perform complex revision hip arthroplasty in January 2019. The use of mixed reality allowed for a very good visualization of the structures and resulted in precise implant fixation. According to the authors' knowledge, this is the first described case report of the combined use of these two innovations. The diagnosis preceding the qualification for the procedure was the loosening of the left hip's acetabular component. Mixed reality headset and holograms prepared by engineers were used during the surgery. The operation was successful, and it was followed by early verticalization and patient rehabilitation. The team sees opportunities for technology development in joint arthroplasty, trauma, and orthopedic oncology.

A complex revision hip arthroplasty was performed using a custom-made implant and mixed reality technology. According to the authors&#39; knowledge, this is the first report of such procedure described in the literature.

The technology of 3D printing and visualization of anatomical structures is rapidly growing in various fields of medicine. A custom-made implant and mixed ...

Sensor Assessment of Gap Balance in Mobile-Bearing Unicompartmental Knee Arthroplasty

The most important procedure of mobile-bearing unicompartmental knee arthroplasty (UKA) is to balance the knee flexion and extension gap. Conventionally, the balance was determined by the subjective assessment of plugging out the feeling gauge. Since it mainly depended on the surgeons' experience, the accuracy was always in doubt. In the past 10 years, pressure sensors have been introduced to guide the gap balance in total knee arthroplasty (TKA). However, the sensor technique was introduced to UKA very recently. Herein is our sensor assessment of the gap balance in 20 cases UKA by one experienced surgeon. The sensor was a custom-designed force sensor matrix according to the shape of the tibial trial of mobile-bearing UKA. The postoperative clinical outcomes and radiographic results were recorded for future comparison. We aim to use this method to assess more than 200 cases of UKA by various surgeons to ultimately standardize the gap-balance result.

Here, we present a protocol to measure the gap contact force and gap balance in mobile-bearing unicompartmental knee arthroplasty (UKA). Along with the clinical and radiographic data, we hope to determine the normal range of the contact force and set up the threshold of the gap balance.

The most important procedure of mobile-bearing unicompartmental knee arthroplasty (UKA) is to balance the knee flexion and extension gap. Conventionally, ...

Augmented Reality Navigation-Guided Core Decompression for Osteonecrosis of Femoral Head

Osteonecrosis of the femoral head (ONFH) is a common joint disease in young and middle-aged patients, which seriously burdens their lives and work. For early-stage ONFH, core decompression surgery is a classical and effective hip preservation therapy. In traditional procedures of core decompression with Kirschner wire, there are still many problems such as X-ray exposure, repeated puncture verification, and damage to normal bone tissue. The blindness of the puncture process and the inability to provide real-time visualization are crucial reasons for these problems.
To optimize this procedure, our team developed an intraoperative navigation system on the basis of augmented reality (AR) technology. This surgical system can intuitively display the anatomy of the surgical areas and render preoperative images and virtual needles to intraoperative video in real-time. With the guide of the navigation system, surgeons can accurately insert Kirschner wires into the targeted lesion area and minimize the collateral damage. We conducted 10 cases of core decompression surgery with this system. The efficiency of positioning and fluoroscopy is greatly improved compared to the traditional procedures, and the accuracy of puncture is also guaranteed.

Augmented reality technology was applied to core decompression for osteonecrosis of the femoral head to realize real-time visualization of this surgical procedure. This method can effectively improve the safety and precision of core decompression.

Osteonecrosis of the femoral head (ONFH) is a common joint disease in young and middle-aged patients, which seriously burdens their lives and work. For ...

The Transition to an Anterior-Based Muscle Sparing Approach Improves Early Postoperative Function but is Associated with a Learning Curve

Surgeons considering transitioning to an anterior-based approach for THA are concerned about the learning curve and the reported marginal clinical benefit. Accordingly, the first cohort of THAs, which were implanted by a single surgeon using the anterior-based muscle-sparing approach (ABMS), was analyzed. The goal of the study was to test 1) whether patient-reported outcomes improved and 2) whether the complication rate decreased with the number of THAs performed. A retrospective cohort study on the first 30 primary THA cases (27 patients) of one surgeon (January 2021-April 2021) using the ABMS approach was conducted. These 30 THAs were compared to 30 primary THA cases (30 patients) done immediately prior to the transition by the same surgeon (September 2020-December 2020) using the posterior approach (PA). The Oxford Hip Score (OHS), Hip Disability and Osteoarthritis Outcome Score (HOOS Junior), and Forgotten Joint Score (FJS) obtained 6 weeks and 6 months after surgery were compared. In addition, three consecutive groups based on equal numbers of THAs were compared for the incidence of complications and surgery time. At 6 weeks after THA, the OHS was 6 points higher after the ABMS approach (p = 0.0408), and the OHS was comparable at 6 months. The HOOS Junior and FJS were similar at 6 weeks and 6 months after surgery.&#160;In the first 10 THAs using the ABMS approach, one patient had a greater trochanter fracture, and one patient had an intraoperative proximal femur fracture. No further immediate interoperative or postoperative complications occurred. Surgery time significantly reduced with the number of THAs performed. Transitioning from the PA to the ABMS approach is associated with a learning curve, which is limited to the first 20 cases. The effect of improved clinical outcomes is apparent within the early postoperative period. After 6 months, THA patients do well regardless of the approach.

The anterior-based muscle-sparing approach for total hip arthroplasty (THA) is associated with a learning curve. However, the improved clinical outcome in the early post-operative phase makes the consideration to transition worthwhile.

Surgeons considering transitioning to an anterior-based approach for THA are concerned about the learning curve and the reported marginal clinical ...

In Vitro Application of a Wireless Sensor in Flexion-Extension Gap Balance of Unicompartmental Knee Arthroplasty

Unicompartmental knee arthroplasty (UKA) is an effective treatment for end-stage anteromedial osteoarthritis (AMOA). The key to UKA is the flexion-extension gap balance, which is closely related to postoperative complications such as bearing dislocation, bearing wear, and arthritis progression. The traditional gap balance assessment is performed by indirectly sensing the tension of the medial collateral ligament by a gap gauge. It relies on the surgeon's feel and experience, which is imprecise and difficult for beginners. To accurately assess the flexion-extension gap balance of UKA, we developed a wireless sensor combination consisting of a metal base, a pressure sensor, and a cushion block. After osteotomy, the insertion of a wireless sensor combination allows the real-time measurement of intra-articular pressure. It accurately quantifies the flexion-extension gap balance parameters to guide further femur grinding and tibia osteotomy, to improve the accuracy of gap balance. We conducted an in vitro experiment with the wireless sensor combination. the results showed that there was a difference of 11.3 N after applying the traditional method of flexion-extension gap balance performed by an experienced expert.

In Vitro Application of a Wireless Sensor in Flexion-Extension Gap Balance of Unicompartmental Knee Arthroplasty

This protocol presents a cadaveric study of a wireless sensor used in medial unicompartmental knee arthroplasty. The protocol includes the installation of an angle measuring device, standardized Oxford unicompartmental knee arthroplasty osteotomy, preliminary assessment of flexion-extension balance, and application of the sensor to measure flexion-extension gap pressure.

Unicompartmental knee arthroplasty (UKA) is an effective treatment for end-stage anteromedial osteoarthritis (AMOA). The key to UKA is the ...

Clinical Application of Artificial Intelligence Preoperative Planning System Combined with Expert Database Retrieval in Complex Revision Hip Surgery

Accurate preoperative planning in revision hip arthroplasty is crucial for achieving successful outcomes. To enhance the intuitive evaluation of acetabular bone defect severity and leverage previous successful experience in revision hip arthroplasty, this study proposes a novel approach based on expert surgical case database retrieval and is initially implemented in clinical application.&#160;In this study, five patients who required revision hip arthroplasty were preoperatively planned to employ the expert case database surgical planning system.The patient&#39;s imaging data was entered into the system and matched with cases in the expert case database. Based on the expert&#39;s surgical experience, a revision surgery plan was recommended. If no suitable case was found, the model and position of the prosthesis were planned based on patient-specific reconstruction results. A total of five patients were enrolled in this study, four males and one female, with a mean age of 50.6 years. The diagnosis was aseptic prosthesis loosening after hip arthroplasty. The mean operative time was 123.2 min, and the mean intraoperative hemorrhage was 672 mL. No intraoperative complications, such as vascular or nerve injury, were observed. In Case 2, for instance, the application of this innovative planning scheme enabled the surgeon to delineate the revision surgery plan for this patient in the preoperative period, thereby reducing the operative time and intraoperative hemorrhage. Furthermore, patients could be apprised of the outcomes of analogous cases in advance. Leveraging a big data analysis approach through our comprehensive case database enables automated identification of matching expert treatment plans throughout the entire process. This particularly benefits inexperienced orthopedic surgeons by providing accurate guidance on surgical strategies to assist them in selecting appropriate prosthetic sizes and mounting positions. Additionally, the matching results can offer patients visualizations depicting predicted postoperative outcomes.

This study proposes a novel artificial intelligence preoperative planning approach based on expert surgical case database retrieval in revision hip arthroplasty. Additionally, the technique was initially employed in five patients, exhibiting a reduction in operative time and intraoperative hemorrhage.

Individualized Stem-positioning in Calcar-guided Short-stem Total Hip Arthroplasty

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