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ORIGINAL ARTICLE

Clinical And Radiographic Short To Midterm Results With The Short Hip Stem Prosthesis "Metha" In 120 Cases

Hans-Georg Simank, Ralph Greiner.

Orthopaedisches Centrum Hochfranken,
Germany.

Address for Correspondence:
Hans-Georg Simank
Orthopaedisches Centrum Hochfranken,
Germany.

E-mail : hans-georg.simank@t-online.de

Abstract:

Aim: The implantation of short stem prostheses in hip arthroplasty is gaining in importance. Because these implants have only become available for a few years, there is little data to facilitate the learning curve and clinical outcome. By nature, therefore, long-term results are missing.

Methods:Clinical and radiographic results and complications are documented in a single surgeon, retrospective study using our own patient population. The study group totals 108 patients receiving 120 short stem implants. Of all treatments (n=120), the data in respect of surgery, perioperative complications, implant size and position are reported. All surgical cases underwent clinical and radiographic follow-up, with complete postoperative reporting on 79 patients for one year, 46 patients for 2 years, and 25 patients for 3 years.

Results: No perioperative or immediate postoperative complications necessitating surgery, such as revisions, infections, etc., occurred in the study group. In one case, the stem had to be replaced after 12 months due to malpositioning. Intraoperatively, there were 2 cases of stem fissure during implantation, both of which were treated by wire cerclage. Subsequent migration was not observed. In one case the stem migrated perioperatively, but spontaneous consolidation ensued thereafter. The Harris Hip Score (HSS) was 92.4 (SD 9.7) at 12 months, 93.8 (SD 11.9) at 24 months, and 94.2 (SD 10) at 36 months. The subjective assessment of satisfaction by all patients was found to be "very satisfied" or "satisfied" at 12 and 24 months. Only one patient was unsatisfied with the outcome.

Conclusions: Overall, this short hip stem prosthesis provides a useful expansion to the prosthetic spectrum. The short-term results are promising and the learning curve acceptable. Combined with a ceramic bearing, it is a favorable option for young and active patients.

J.Orthopaedics 2010;7(4)e8

Keywords:

arthroplasty; hip; short stem; Metha

Introduction:

The implantation of short stem prostheses in hip arthroplasty is gaining in importance1. This is reflected by an increasing number of surgical procedures, as well as an increasing number of implant models available on the market1. The anticipated advantages are seen in smaller sized implants which help to reduce the loss of bone and support metaphysical anchorage. In addition, the prostheses are also well suited to implantation with less invasive procedures. There are drawbacks, however, in that the implants are relatively new to the market and consequently little data is available on early risks and complications (learning curve). Long-term results are lacking therefore1.
We report on our initial experience and results with the Metha modular short hip stem prosthesis over a maximum follow-up period of about 3 years, paying special attention to early problems.

Materials and Methods:

This study included all patients receiving a short hip stem implant (Metha, B. Braun Aesculap, Tuttlingen/ Germany) in our department between the beginning of July 2006 and March 2010. All patients were under the care of one surgeon (HGS), underwent conservative pre-treatment and were suffering from advanced, painful coxarthrosis (stage IV) as evidenced clinically and radiographically.

The exclusion criteria covered male patients aged over 68 and female patients over 60, poor bone quality or anatomical variants which complicate implantation of a short stem prosthesis (severe Coxa vara or valga, severe antetorsion), status post fracture of the coxal femur, post infection or post tumor. In all cases planning ensued preoperatively, the surgical approach was less invasive 1 and in a supine position, and the implant position was basically controlled intraoperatively by X-ray. Postoperatively, the patients were asked not to strain the operated leg with more than 20 kg in the first 6 weeks, after which they underwent radiographic follow-up, and total loading was permitted.

All patients underwent clinical and radiographic follow-up in order to identify all immediate perioperative complications. The postoperative findings are recorded as Harris hip scores (1969) 1. The postoperative X-rays were analyzed in both planes using the Gruen zone system (1979) 2. Zones 1, 2 and 6, 7 were defined on the coated area of the short stem, and zones 3, 4 and 5 on the distal, uncoated area. Periarticular ossification was classified according to Brooker (1973)3.

Results :

The study group includes 120 cases of short stem implant. Of all treatments (n=120), the data in respect of surgery, perioperative complications, implant size and position are reported. All cases were monitored clinically and radiographically for a follow-up period of at least 3 months and maximally 36 months.

The mean age of the entire population (n=120) was 54 years (35.9-67.3). There were 52 women and 56 men, with a mean weight at the time of surgery of 88.2 kg (55-134), equivalent to a mean BMI of 31 (23-47). The surgical indication was idiopathic coxarthrosis in 72%, hip dysplasia in 18%, femoral head necrosis in 6%, and other indications in 4%.

Postoperatively, full follow-up data are available for 79 patients at 12 months, 46 patients at 24 months, and 25 patients at 36 months. The Harris Hip Score (HSS) was 92.4 points (SD 9.7) at 12 months, 93.8 points (SD 11.3) at 24 months and 94.2 points (SD 10) at 36 months postoperatively. The subjective judgment of satisfaction by all patients in the group at 12 to 36 months was "very satisfied" in 75%, and "satisfied" in 24%. Only one patient was dissatisfied with the outcome. 76.0% (91) of patients claimed to have "no pain or ignorable pain", 16.0% (19) "occasional or mild pain/minimal pain", and 8.1% (10) described "tolerable or moderate pain". No patient had "serious pain" or "total disability". The mean degree of motion improved in all patients by the last follow-up examination, reaching mean values of 109 degrees of flexion (90-130 degrees), 36 / 0 / 19 degrees of abduction/adduction (10-60 / 10-30 degrees) and 20 / 0 / 27 degrees of inner rotation/outer rotation (5-40 / 10-40 degrees).

No radiolucencies are found at any time, in any patient, in the Gruen zones of the metaphysically coated stem component (AP and lateral projection) on radiographic analysis (Fig. 1a). In 75% of cases (n=90) the tip of the implant reaches the lateral corticalis on AP projection. In the transition of the coated margin, 71% of cases reveal medial, and 62% lateral densification zones at 12 months with alignment of the bone structures (AP projection) to the implant surface. At 24 months, 82% of cases show medial, and 74% lateral densification zones. Osteointegration, with reorientation of the trabeculae, was found in all cases at 12 months (Fig. 1b).

Fig. 1: a) Lack of lucencies in the Gruen zones on 2-year follow-up. b) Alignment of trabecular structures

Computer-assisted review of the postoperative pelvic imaging revealed restoration of leg length in 107 cases, and leg lengthening of up to 0.8 cm in 4 cases, 0.8-1cm in 6 cases, and 1 - 1.5 cm in 2 cases. In one case the stem had migrated approximately 1cm during the 6 weeks postoperatively. No further migration is seen in subsequent controls; the cause was found to be an undersized implant. The patient is free of symptoms (Fig.2).

Fig. 2: Postoperative migration of stem with stabilization on follow-up

The majority of the implants proved to be of moderate size, as described in the literature [[i]]. In 39.8% (48) of cases 130° neck adapters were used, in 53.4% (64) 135°, and in 3.4% (5) 140°. Only in 1.4% (1) was an antetorsion version, and in 2.2% (2) a retrotorsion version selected. In 92.5% of cases ceramic-on-ceramic bearings were chosen, and in 7.5% of cases a PE-on-ceramic bearing whereby optimal positioning of the cup was not always possible (Fig. 3).

Fig. 3: AP and lateral view of a typical Metha short hip stem implant

No perioperative or postoperative complications necessitating surgery, such as revisions, infections, etc., occurred. Intraoperatively, stem fissure resulted in 2 cases during implantation of the prostheses, both of which were medial in the direction of the lesser trochanter. Both cases were treated by wire cerclage. Subsequent migration was not observed. In one case involving a heavily obese female patient, the consolidated stem had to be replaced after about 12 months by a cementless standard stem on account of postoperative, initially unnoticed malpositioning and increasingly severe symptoms. Replacement with a standard straight stem was possible without complications (Fig. 4). Heterotopic ossification > Brooker 2 was not found in this study.

Fig. 4: Revision of a malpositioned short stem after 12 months, replaced by a straight stem (CLS).

Discussion :

Our initial results with the Metha short hip stem prosthesis are encouraging with a view to the perioperative rate of complications. The learning curve is acceptable. Of the first 120 implantations, there were 2 stem fissures which could be safely treated by cerclage and remained stable without the need for further intervention. In one additional case the chosen prosthesis was too small and resulted in migration of the stem (Fig. 2). The implant stabilized spontaneously thereafter. As experience was gained, fewer such problems arose. Fissuring of the stem is also a well-known phenomenon with established implant models, however. Only in one case the stem had to be replaced as a result of initially unnoticed malpositioning in an overweight female patient. Replacement with a standard straight stem was possible in this case without complications. To begin with, there was a relatively high percentage of suboptimal stem positioning without lateral corticalis contact (25% of all cases). All of these stems could be easily consolidated, however. Introduction of a modified insertion instrument rendered implantation of the prosthesis more straightforward and reduced the likelihood of valgic implantation without guaranteed lateral corticalis contact. After such modification, the tip of the implant abuts with the lateral corticalis in virtually all cases.

The clinical results, measured by Harris Hip Score and visual analog scale for pain, are found to equate with the good results already known for conventional and minimally invasive hip arthroplasty [[i], [ii], [iii], [iv]]. Harris hip scores of > 90 points were achieved at 12 and 36 months postoperatively. One fact which is certainly favorable is the configuration of the prosthesis, which enables preservation of bone stock at the greater trochanter area and facilitates a minimally invasive approach while sparing the gluteal musculature.

We recorded two cases of leg lengthening of over one centimeter more than the opposite side using computer-assisted analysis of the postoperative pelvic X-rays. Severe bilateral dysplasia of the hip joint was found in one of these clinically significant cases. The lengthening was accepted on the reasons of stability. Since the femoral ring should be completely preserved for the purpose of primary stability, restoration of leg length may entail certain problems since extension tends to result from a short femoral neck due to the inevitable preservation of the femoral ring even when using a short head. This should be considered during preoperative planning.

Overall, this short hip stem prosthesis provides a useful expansion to the prosthetic spectrum. The short-term results are promising and the learning curve acceptable. Its design enables preservation of the bone stock of the greater trochanter and selection of an approach which conserves the soft tissue. The alignment of the bone structures appears to confirm the assumption of proximal force transmission, as was also shown by the Santori et al. study team [[v]]. Combined with a ceramic bearing, it is a promising option for young and active patients [[vi], [vii]]. However, patients need to be fully informed that so far no long-term results are available for such an implant.

Reference:

  1. Buecking PK, Feldmann P, Wittenberg R. Metha - Modulare Kurzschaftprothese. Orthop. Praxis 2006; 8: 474-477

  2. Morrey BF, Adams RA, Kessler M. A conservative femoral replacement for total hip arthroplasty. A prospective study. J Bone Joint Surg Br. 2000; 82(7):952-958

  3. Stukenborg-Colsman C. Schenkelhalsendoprothesen. Orthopäde 2007; 36(4):347–352

  4. Hube R, Zaage M, Hein W, Reichel H. Frühe funktionale Ergebnisse einer Kuzschaftprothese des Hüftgelenks mit metaphysär-intertrochantärer Verankerung. Orthopäde 2004 Nov;33(11):1249-1258

  5. Engh CA, Bobyn JD, Glassman AH. Porous-coated hip replacement: the factors governing bone ingrowth, stress shielding and clinical results. J Bone Joint Surg 1987; 69-B: 45-55

  6. C. V. Albanese, Lucidi M, Rendine M, Santori N, Pavan L, Passariello R, Santori FS. Effect on bone mineral density of progressive shortening of the femoral stem in a short stemmed prosthesis evaluated by DXA. JBJS Britisch Volume 2009, V91-B, Issue suppl_I, 145

  7. Wollmerstedt N, Nöth U, Mahlmeister F, Lotze A, Finn A, Eulert J, Hendrich C. Aktivitätsmessung von Patienten mit Hüfttotalendoprothesen. Orthopäde 2006; 35(12):1237-45

  8. Eben R. Walk B. Summer S. Maier M. Thomsen P. Thomas. Implantatallergieregister – ein erster Erfahrungsbericht. Orthopäde 2009, 38:557–562

This is a peer reviewed paper 

Please cite as: Hans-Georg Simank: Clinical And Radiographic Short To Midterm Results With The Short Hip Stem Prosthesis "Metha" In 120 Cases.

J.Orthopaedics 2010;7(4)e8

URL: http://www.jortho.org/2010/7/4/e8

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