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abstract

10-Year Experience With Short Stem Total Hip ArthroplastyGABRIELA VON LEWINSKI, MD; THILO FLOERKEMEIER, MD

Since 1998, short stem total hip arthroplasty (THA) has been performed at the authors’ institution. Currently, 30% of THAs are performed with short stems. This article reports on complications that required revision of a short stem THA. Between September 2005 and February 2012, a total of 1953 Metha short stem THAs were performed; of these, 38 required revision due to mechanical complications. In 12 cases, the modular tita-nium neck adapter failed. In 19 cases, aseptic implant loosening occurred; of these, 11 cases were due to major stem subsidence. In 2 cases, via falsa (cortical penetration) implantation occurred. In 5 cases, periprosthetic fractures led to revision. This corre-sponds to an aseptic total revision rate of 1.3% for 26 short stems and 1.9% including the cases of all 38 documented revision cases. Thirty-four cases were revised with cementless standard hip stems, 2 cases were revised with short stems, and 2 cases were revised with long revision stems. Undersizing was analyzed in 58% of aseptic revisions. Fifty-four percent of revisions were performed in male patients — 23% with osteonecrosis of the femoral head, and 7% with short hip stems positioned in varus in coxa vara deformities. Seventy-two percent of revisions after marked early stem sub-sidence and position change into valgus were performed in female patients. Dysplastic hips with coxa valga did not show elevated revision rates. No revisions were per-formed for dislocation or femoral thigh pain. Short stem THA with the Metha implant is a bone-preserving option for various indications in select patient groups.

The authors are from the Department of Orthopaedic Surgery, Hanover Medical School, Hanover, Germany.

Dr. von Lewinski received a grant, payment for lectures, and payment for travel expenses from B. Braun Aesculap. Dr. Floerkemeier receives payment for lectures from B. Braun Aesculap.

Correspondence should be addressed to: Gabriele von Lewinski, MD, Department of OrthopaedicSurgery, Hannover Medical School, Anna-von-Borries-Str, 1-7, 30625 Hannover, Germany (Gabri-

ela.lewinski@ddh-gruppe.de).doi: 10.3928/01477447-20150215-57

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Short stem total hip arthroplasty (THA) is an established proce-dure. Studies of short stem THA

have shown a less pronounced loss in bone mineral density around the proxi-mal femur,1 good short-term results in patients with femoral head osteone-crosis,2 and good mid-term results in young patients who require THA.3 Such femoral implant components present a bone-preserving alternative to standard length stems and offer the opportunity for revision with a standard length stem if needed. Studies have investigated the migration patterns of short hip stems with radiostereometric analysis ,4 the in-fl uence of resection height to the proxi-mal load transfer,5 fi nite element analy-sis of short stems,6 and biomechanical comparisons to standard stems.7

Since 2005, the Metha short stem (Aesculap AG, Tuttlingen, Germany) has been used at the authors’ institution; more than 2,000 cases have been performed us-ing an anterolateral (30%) or transgluteal approach (70%). As the implant range of modular and nonmodular components changed over the years, 190 short stems with a modular titanium neck adapter were implanted in 2005 and 2006, and 380 short stems with modular cobalt-chromium neck adapters were implanted since 2007. Since 2008, the majority of implanted short hip stems used nonmodu-lar monoblock components, with the total number of such THAs being more than 1,500. The femoral component design, shape, and instrumentation have remained unchanged since 2004.

The percentage of short stem THAs increased from 10% during the fi rst year of introduction to more than 30% in 2009. Based on positive clinical experiences, cementless short stem THAs currently ac-count for approximately one third of pri-mary cementless THAs performed at the authors’ institution (Figure 1).

For all short stem THAs that required revision, a detailed case analysis was per-formed to learn from femoral component

failures. Such analysis of adverse events in short stem THA is an effective tool to identify risk factors, possible contraindi-cations, and surgery-related aspects. In cases of implant revision, the reason for failure and any strategy to avoid such cases in the future is mandatory when a new implant concept is introduced. This should lead to a better understanding of the limitations for short stem THA and improved preoperative assessment of in-dications and differentiation for standard and short stem THA in each patient. The

purpose of this study was to analyze the revisions that occurred with the Metha short stem at the authors’ institution.

MATERIALS AND METHODSSince the Metha short stem THA was

fi rst performed, all revisions were docu-mented. Patient age, gender, body mass index (BMI), and preoperative indica-tion for the index surgery were reviewed. When such stem revisions became neces-sary, implant selection at index surgery was reassessed in detail. Radiographic

Figure 1: Chart showing the number of Metha short stems and total number of total hip arthroplasties (THAs) (N=1953) from 2005 to 2013.

Figure 2: Chart showing the distribution of short hip stem revisions according to type of complication.

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documentation was evaluated regarding sizing of the implant and its relation to bone quality and individual patient anato-my, as well as osteotomy level and prima-ry implant position. Preoperative planning was reassessed and compared directly with the postoperative results. Operative details and events also were reviewed. All aspects that might have led to revision as well as the types of femoral revision im-plants were documented.

RESULTSFrom 2005 through 2013, a total of

1953 patients underwent short stem THA; of these, 45 THAs required revision. Seven revisions were performed because of infection, and 38 revisions were per-formed because of mechanical complica-tions (Figure 2). The fi rst revision was performed in September 2005, and the last revision was performed in February 2012. Failure of the modular titanium neck adapter required revision in 12 patients. Aseptic implant loosening required revi-sion in 19 patients; of these, major stem subsidence occurred in 11 patients. Two

cases required revision due to via falsa implantation. Five periprosthetic fractures led to revision. There were no dislocations or revisions due to thigh pain.

Based on the total number of 190 modular stem components with titanium neck adapters implanted during 2005 and 2006, the 12 modular titanium neck fail-ures correspond to a rate of 6.3%, with an average time to failure of 57.7 months (minimum and maximum of 19.5 and 88.3 months, respectively). Excluding these failures of 12 modular neck adapt-ers, the average time to implant revision for the remaining 26 revision cases was 8.9 months (minimum and maximum of 0.4 and 28.5 months, respectively). The revision rate of short hip stems im-planted since 2005 and revised through 2013 was 1.9%, including all 38 docu-mented revision cases of 1953 implanta-tions, and 1.3% without the 12 failures of the modular titanium neck adapter of the fi rst implantation series. Thirty-four cases were revised with cementless stan-dard hip stems, 2 short stems, and 2 long revision stems.

The yearly number of revisions ex-cluding modular titanium neck adapt-er fractures ranged between zero and 1.9% during the 9-year period (Table). Twenty of the 26 short stem revisions were necessary within the fi rst year af-ter the index THA. Five of the remaining 6 revisions occurred within the second year. Aseptic loosening of the short hip stem was differentiated into cases with marked postoperative subsidence >10 mm and a group of implants with lesser subsidence. For aseptic loosening, 11 of 19 cases were identifi ed as undersized. The patients with subsidence >10 mm showed a valgus position after subsid-ence, whereas the patients who demon-strated loosening with less subsidence failed into a varus position.

Twenty-three percent (6 of 26) of re-visions occurred in patients with osteone-crosis of the femoral head. Other indica-tions such as dysplastic hips with a coxa valga did not show an elevated revision rate, but 7% of revised hips were in pa-tients with a short hip stem positioned in varus for coxa vara deformity.

Table

Overview of Complications Leading to Metha Short Stem Revision

2005 2006 2007 2008 2009 2010 2011 2012 2013

Short stem implantation 76 114 168 225 333 304 275 253 205

Aseptic loosening 0 0 0 0 0 5 1 2 0

Undersized stem 0 1 3 0 4 3 0 0 0

Periprosthetic fracture 0 1 0 1 1 2 0 0 0

Titanium neck adapter failure 5 7 0 0 0 0 0 0 0

Via falsa 0 1 0 1 0 0 0 0 0

Total number of short stems 76 190 358 583 916 1220 1495 1748 1953

Total number of revisions 5 15 18 20 25 35 36 38 38

Total number of titanium neck adapter failures 5 12 12 12 12 12 12 12 12

Revision rate for all cases 6.6% 7.9% 5% 3.4% 2.7% 2.9% 2.4% 2.2% 1.9%

Revision rate without titanium neck failures 0% 1.6% 1.7% 1.4% 1.4% 1.9% 1.6% 1.5% 1.3%

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Although a higher percentage of wom-en underwent THA with a short stem, 54% of the patients who required revision were men. Also, in the group of titanium

neck failures, 10 of 12 patients were men. In patients with loosening into varus posi-tion, the percentage of men with coxa vara was 88% (7 of 8). In contrast, for patients

in the subsidence or valgus group repre-sented, 73% were women. Within this group, 45% of patients had osteonecrosis of the femoral head and 45% of patients had a high BMI (>35) as well.

Of 5 periprosthetic fractures, 1 fracture occurred in a patient with osteonecrosis of the femoral head. Two fractures occurred after more than 2 years and were linked to trauma. One fracture was associated with an immediate postoperative failure and was believed to be the result of an in-traoperative femoral fi ssure that was not diagnosed. Intraoperative unstable small fi ssures typically are treated with a wire cerclage. Cases of a rotationally stable rasp are only treated with partial load bearing, and revision following this has not occurred. Two revisions were neces-sary for unrecognized via falsa positions, with one lateral and one dorsolateral corti-cal penetration of the short stem.

Case ExamplesThe following case examples show

typical failure situations that can be pre-vented by systematic intraoperative as-sessment of implant size and position. Undersizing is the most common com-plication; cortical contact inside the neck must be observed. It is helpful to check the lateral view intraoperatively. Cancel-lous stem fi xation should be avoided as this could give an impression of a nonex-isting primary stability.

To follow the Metha short stem an-choring concept, it is essential to have a lateral neck support inside the closed fem-oral neck osteotomy. This support must be assessed during surgery and is infl uenced by stem sizing and depth of implantation.

High Osteotomy and Undersizing. A high osteotomy can lead to a varus and undersized position of the stem (Fig-ures 3-5). Each osteotomy level requires a dedicated position and sizing. Ensured primary stability is essential for similar reconstructions.

Aseptic Loosening. In cases with miss-ing primary stability, the implant has no

Figure 3: Preoperative anteroposterior radiograph of a 57-year-old man with a body mass index of 39 showing a slight dysplastic coxarthrosis (A). Immediate and 1-week postoperative anteroposterior radiographs showing implant position after arthroplasty with a Metha short stem (B, C). Postoperative anteroposterior radiograph showing revision to a standard length stem after 2 weeks due to undersizing of the Metha short stem (D).

DA B C

Figure 4: Postoperative anteroposterior radiographs of a 48-year-old man with a body mass index of 42 and coxarthrosis showing implant position at immediate postoperative (A), 2 weeks (B), and following revision at 3 months due to undersizing and lack of lateral neck support (C).

A B C

Figure 5: Postoperative anteroposterior radiographs of a 59-year-old man with a body mass index of 30 and slight varus coxarthrosis showing implant position after arthroplasty with a Metha Mono 130° short stem at immediate postoperative (A),1 week (B), 6 months (C), and following revision at 6 months due to high osteotomy and undersizing (D).

A B C D

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chance to grow in and needs to be revised early. If the stem does not subside or stabi-lize, pain and radiographic signs of loos-ening present a clear indication for revi-sion (Figure 6).

Via Falsa. In case of a via falsa pen-etration of the rasp or implant through the femur, change to a standard length stem is recommended as long as the penetration is in Gruen zone 3 (Figure 7). In all other zones, there is a high potential to use still a Metha stem.

Correct Implant Positioning. The me-dial part is supported by the calcar region and the distal part of the implant touches the lateral cortex of the femur (Figure 8). In the axial view the implant has to follow the an-teversion of the femoral neck.

DISCUSSIONWhen developing a new surgical meth-

od, it is mandatory to systematically ana-lyze failures to speed the learning process and to confi rm or revise indications, tech-nique, and implants to limit patient harm as much as possible. As all surgery is linked to a certain percentage of failure in all dis-ciplines, care must be taken to identify dif-ferences in complication rates between the established and the new operative therapy. As adverse events normally are seldom in THA, the differentiation process requires a limited number of events for the differ-ence to become obvious or even signifi -cant. Manufacturers responsible for the technical function of instruments and im-plants and surgeons therefore must watch all adverse events from the beginning with concentrated attention, comparing failure rates continuously as closely as possible to established practices, optimally within the frame of a clinical study, with rigorous rules of observation.

This retrospective revision analysis of femoral complications is based on a high number of cases and a certain level of experience with short hip stems, which is indicated in one third of the primary THAs performed at the authors’ institu-tion. Since only the revision cases treated

at the authors’ institution were included in this analysis, the total number of revisions may be higher. However, the fi ndings of the particular reasons for femoral component revision in this analysis are believed to be representative for the Metha hip implant.

Other studies have reported that implant undersizing resulted in reduced primary stability with early stem subsidence.8 In one of the fi rst studies of Metha short-term results, Braun and Sabah9 identifi ed risk factors as stem undersizing, varus position-ing, and missing proximal lateral cortex contact within the closed neck. Via falsa stem implantations have been reported by Wittenberg et al10 in 2 of 250 cases and in a single case by Milecki et al.11

In a report of cone fractures among patients treated with the modular tita-nium alloy neck adapter, a combination

of different parameters was identifi ed as risk factors of implant failure immediate-ly after occurrence of an elevated cone fracture rate, including intraoperative

Figure 8: Postoperative anteroposterior (A) and lateral (B) radiographs of a 62-year-old man with coxarthrosis showing a well-positioned Metha short stem.

A B

Figure 7: Preoperative anteroposterior radiograph showing a 50-year-old woman with osteoporotic cox-arthrosis (A). Postoperative anteroposterior radiographs showing implant position after arthroplasty with a Metha short stem at immediate postoperative (B) and 3 months (C). Postoperative anteroposterior radiograph showing dorsolateral penetration at 36 months (D).

A B C D

Figure 6: Preoperative anteroposterior radiograph of a 63-year-old man with a body mass index of 30 showing coxarthrosis (A). Postoperative anteroposterior radiographs showing implant position after ar-throplasty with a Metha Mono 135° short stem at immediate postoperative (B) and 6 months (C), and following revision at 8 months due to aseptic loosening (D).

B CA D

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particle contamination of the cone, con-nection, excessive loading due to a pa-tient weight >100 kg or high activity lev-el, and male gender. An additional risk was a cone adapter of 135° and 130°.12 Revision of well-fi xed femoral short stem components could be performed with conventional standard stems.13 Since the modular neck adapter was changed to a cobalt-chromium material in 2007 and the availability of nonmodular stems, the majority of short stem THAs performed at the authors’ institution are the non-modular type.

Selection of the correct femoral stem size for any individual patient is impor-tant in THA, for standard and for shorter stems during preoperative planning.14 Although a standard stem must follow the orientation of the femoral diaphy-sis, a short stem achieves a metaphyseal anchorage with an orientation along the antetorsion of the femoral neck. This difference might play a role in size and alignment errors that were observed ini-tially when using this new type of im-plant. These errors may infl uence later aseptic loosening but often are linked to early implant migration, which has occurred as one of the most frequent adverse events. Preoperative templating for short stems and a detailed analysis of the individual patient anatomy in antero-posterior and lateral views can predict the correct implant size more accurately compared to preoperative templating only in the anteroposterior view.

When evaluating revisions from 2005 to 2013, a further observation emerged. In 2011, a quality management program was initiated for arthroplasty surgeries of the knee and hip. From this time point on, only surgeons with a total number of more than 50 operations of either total hip or knee arthroplasties were allowed

to perform the operations. This reduced the total failure rate of all short stem im-plantations from 1.9% in 2010 to 1.3% in 2013. This fi nding emphasizes the im-portant role of experience and training in surgery, and has shown a measurable effect on the revision rate at the authors’ institution.

CONCLUSIONThe Metha short stem is a bone-pre-

serving option for various indications and younger patient groups when follow-ing the special requirements of a short stem with regard to specifi c patient anat-omy and biomechanics. It offers advan-tages when small diaphysis or dysplas-tic hips are being treated. The observed complication rates compare favorably with conventional THA. However, early failures due to undersizing and malposi-tioning seem to be more relevant in short hip stems. Special attention is needed if surgeons are not yet familiar with the technical differences compared to con-ventional THA.

REFERENCES 1. Lerch M, von der Haar-Tran A, Windhagen

H, Behrens BA, Wefstaedt P, Stukenborg-Colsman CM. Bone remodelling around the Metha short stem in total hip arthro-plasty: a prospective dual-energy X-ray absorptiometry study. Int Orthop. 2012; 36(3):533-538.

2. Floerkemeier T, Tscheuschner N, Callies T, et al. Cementless short stem hip arthro-plasty METHA as an encouraging option in adults with osteonecrosis of the femo-ral head. Arch Orthop Trauma Surg. 2012; 132(8):1125-1131.

3. Thorey F, Hoefer C, Abdi-Tabari N, Le-rch M, Budde S, Windhagen H. Clinical results of the Metha short hip stem: a per-spective for younger patients? Orthop Rev (Pavia). 2013; 5(4):e34.

4. Flörkemeier T, Schwarze M, von Lewinski G, et al. Analyse der Migration der Metha-Kurzschaftprothese mittels Radiostereomet-rie - vorläufi ge Ergebnisse einer klinischen

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6. Lerch M, Weigel N, Windhagen H, et al. Finite element model of a novel short stemmed total hip arthroplasty implant developed from cross sectional CT scans. Technol Health Care. 2013; 21(5):493-500.

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14. Schmidutz F, Steinbrück A, Wanke-Jellinek L, Pietschmann M, Jansson V, Fottner A. The accuracy of digital templating: a com-parison of short-stem total hip arthroplasty and conventional total hip arthroplasty. Int Orthop. 2012; 36(9):1767-1772.

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