The Knee 16 (2009) 46–49
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The Knee
Trabecular metal patella in total knee arthroplasty with patella bone deficiency D. Tigani ⁎, P. Trentani, F. Trentani, I. Andreoli, G. Sabbioni, N. Del Piccolo VII Department of Orthopaedic Surgery, University of Bologna, Rizzoli Orthopaedic Institute, Bologna, Via Pupilli 1, 40136, Bologna, Italy
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Article history: Received 29 April 2008 Received in revised form 21 August 2008 Accepted 22 August 2008 Keywords: Patella Bone loss Total knee arthroplasty Trabecular metal
a b s t r a c t This study evaluates results following patellar resurfacing using trabecular metal (TM) patella in marked deficiency or weakness of patellar bone that precludes patellar resurfacing with a standard cemented patellar button. Ten consecutive patients undergoing primary (3 cases) or revision (7 cases) total knee arthroplasty with patella augmentation were evaluated at a mean follow-up of 45 months (range 18–65). Nine patients had marked patellar bone deficiency and one had had previous patellectomy. No intra-operative complications occurred. There was no displacement of the patellar component and no patellar fractures when at least 50% of bone contact was possible. We observed loosening of the patella augmentation 17 months after the index procedure only in the case of previous patellectomy. When bone was present the fixation appeared excellent by radiographic evaluation already at 3 to 6 months after surgery; afterward bone contact was uniform in the peripheral regions in both lateral and Merchant radiographic views without signs of loosening. Finally, the mean Knee Society scores improved in all patients. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Compromised patellar bone stock poses significant technical problems in primary and revision knee arthroplasty. In revision knee surgery bone deficiency is normally secondary to loosening of the patellar button and osteolysis that affects severely the patella. In primary cases it is rare that the patella has been so eroded that resurfacing is not possible. This happens in severe patello-femoral arthritis or inflammatory arthropathy, when the patella may be thin and track laterally before and during arthroplasty. In these cases traditional approaches have included non-resurfacing, thus leaving a thin patellar shell, or total patellectomy [1,2]. Both solutions have been associated with lower functional results compared with resurfaced patella. Recently, a patellar bone grafting procedure has been described to provide patellar bone for possible future revision [3]. The “gullwing” patellar osteotomy [4] has also been proposed in case of low demand patients, whereas in some cases it is possible to rebuild a damaged patella with K-wires in a reinforcing configuration to support the pegs of the patellar implant using the so called “rebar” technique [5]. A new material, trabecular metal (TM), made using tantalum metal and the vapour deposition technique to create a metallic configuration with 80% porosity, and physical and mechanical properties similar to bone introduced in the late nineties [6–9]. The aim of this study was to evaluate the results of TM patella augmentation in primary and revision total knee arthroplasty (TKA) in patients with
⁎ Corresponding author. Tel.: +39 0516366252; fax: +39 0516366840. E-mail address:
[email protected] (D. Tigani). 0968-0160/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2008.08.005
marked patellar bone loss or poor bone quality that precludes patellar resurfacing. 2. Materials and methods 2.1. Study group A cohort series of 10 consecutive patients, with at least 18 months of follow-up, treated with trabecular metal augment patella for marked deficiency or weakness of patella that precluded patella resurfacing with a standard cemented patellar button, made the basis of the present study. All the operations were performed by a single surgeon (DT) from February 2003 to March 2007. Three patients underwent primary TKA whereas seven knees were submitted to a revision procedure. In all cases the decision to implant the TM patella was made during surgery according to the residual amount and consistency of the patellar bone. In the primary group the diagnosis was poliomyelitis with multidirectional knee instability in two cases and severe arthritis in valgus knee with a thin patella tracking laterally in one patient that had already had a tibial tubercle realignment. The two poliomyelitis patients received a rotating hinge knee prosthesis (Nex Gen RHK, Zimmer, Warsaw, USA). The third patient underwent a primary posterior stabilized arthroplasty (Nex Gen Legacy, Zimmer, Warsaw, USA). In the revision group all patients underwent femoral and tibial revision at the time of TM patella implantation. Four patients were affected by aseptic loosening of previous implants, one reported the hardware failure of a megaprosthesis ten years after an en bloc resection for tumor and two cases presented a malrotation of at least one of the components. In this group three patients had already
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undergone patellar resurfacing, which had resulted in marked patellar bone loss, another patient was previously submitted to patellectomy, whereas in the remaining three patients the patella was so eroded and thin that standard resurfacing was no possible. A rotating hinge knee arthroplasty (Nex Gen RHK, Zimmer, Warsaw, USA) was used in four patients, two cases received a modular condilar constrained prosthesis (Nex Gen LCCK, Zimmer, Warsaw, USA). Finally, one patient was treated for hardware failure of a megaprosthesis ten years after an en bloc resection for tumor. At the time of revision, both femoral and tibial components were loosed and then revised with a modular rotating hinge megaprosthesis (GMRS Stryker-Howmedica, Usa). As the patella was extremely dug out, long, thin and tracking laterally, an augmented patella was implanted in the half upper pole of the residual bone (Fig. 1A–B). Demographic data for the study groups are shown in Table 1. 2.2. Surgical technique In all cases where some amount of bone was present the remaining shell was reamed using an appropriate diameter-hemispherical reamer in an attempt to provide a healthy hemispherical surface for the attachment of the trabecular metal shell. Trials were made to restore normal patellar thickness, the metal base-plate was then placed on the residual bone and fixed with a non-absorbable suture
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Table 1 Demographic data of primary and revision groups
1 2 3 4 5 6 7 8 9 10
Age/gender
Diagnosis
Prosthesis
FU
Primary or revision
56/M 54/F 68/F 65/M 73/F 77/M 76/M 77/F 45/M 78/F
Polio Polio OA Loosening Loosening Loosening Malrotation Malrotation Hardware failure Loosening
Zimmer RHK Zimmer RHK Zimmer LPS Zimmer RHK Zimmer RHK Zimmer RHK Zimmer LCCK Zimmer LCCK Stryker GMRS Zimmer RHK
57 63 36 56 60 17 failure 60 65 32 18
Primary TKA Primary TKA Primary TKA Revision Revision Revision Revision Revision Revision Revision
through the holes of the peripheral tantalum ring. The reconstruction was completed by cementing the polyethylene patellar component into the trabecular metal surface. Eight patients received a medium-sized trabecular metal patella (five were 19.5 mm thick and three were 22 mm thick and made from a combination of metal and polyethylene), and two patients received a large 20 mm thick patella. After surgery, patients were treated with a routine total knee replacement protocol that consisted unrestricted passive and active assisted range of motion, isometric muscular exercises and
Fig. 1. (A) Lateral radiograph showing hardware failure of the femoral stem and patella extremely dug out, long and thin. (B, C) Lateral radiograph following revision TKA with a trabecular metal patellar implant at 3 and 24 months.
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2.3. Post-operative assessment The American Knee Society Score (AKSS) was used to assess clinical results [10]. AKSS is supported by three general categories, depending on whether other joints are involved or medical infirmity is present. The scoring system provides two scores, total knee score and functional score. Hospital for Special Surgery (HSS) patella score was employed to evaluate patello-femoral outcome which consists of both subjective and objective tests [11]. 2.4. Radiographic assessment Fig. 2. Merchant view of patella after revision TKA with TM shell.
ambulation using a walker or crutches with weight bearing as tolerated.
Radiographic assessment included an anteroposterior view, a lateral view and a skyline view with 45° of knee flexion. Lateral tilt and patellar displacement were recorded according to the method described by Gomes et al. [12]. Lateral tilt was defined as the angle between a line from the anterior limit of the femoral condyles and a
Fig. 3. (A) Pre-operative lateral radiograph of a 73-year-old man who had previously undergone patellectomy. (B) Post-operative lateral radiograph showing placement of TM patellar component. (C) Merchant view performed 17 months showing displacement of the patellar component.
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line drawn through the metal base-plate of TM patella and the polyethylene button. Patellar displacement was measured as the distance between the center of the patella and a line drawn through the central area of the femoral condyles. 3. Results There were no revision undertaken in the patients were residual patellar bone was present. The patient who had previously undergone patellectomy developed loosening of the patellar component 17 months after trabecular metal reconstruction. The patient was treated by removal of the trabecular metal implant, and imbrication of the two capsular flaps on the medial and lateral sides to tighten up some of the slack. No intra-operative complications connected with the implantation of the trabecular metal patella were observed. Post-operative complications included one case of temporary palsy of the peroneal nerve with total recovery after 6 months, and one case of deep vein thrombosis. According to the American Knee Society Score general categories one patient belonged to type A, five to type B and three to type C. The mean Knee Society Score improved significantly from a mean of 40.8 (range 0 to 55) to 88.8 (range 75–95) at the last follow-up. The functional score improved from a mean of 47 (range 0 to 75) to 79.4 (range 65 to 95). The average pre-operative range of motion was 79.5° (range, 40°–110°), whereas the average post-operative range of motion was 105 (range, 90°–120°). Extensor lag was present pre-operatively in 6 cases ranging from 5° to 15°. Only one patient presented an extensor lag of 5° post-operatively. At the most recent follow-up the HSS patellar score averaged 88 (range 75 from 100). Moderate anterior knee pain (VAS = 5) when rising from a chair for three times was present in one patient, and mild pain (VAS = 3) occurred in another two patients. There were no cases of severe pain. If we exclude the two poliomyelitis patients, who presented some difficulty in climbing or descending stairs, no limitations were found for the other patients. Of the objective point of view any cases of tenderness or crepitus was present. The quadriceps strength was deficient in two cases (poliomyelitis patients), reduced in two and normal in the remnant patients. There was no displacement of any trabecular metal patellar component when residual bone was present. In these cases the radiographic follow-up assessments showed evidence of uniform bone contact in the peripheral zones in both lateral (Figs. 1 and 2) and Merchant radiographic views already between 3 and 6 months (Fig. 3). Afterward there was no evidence of radiolucency and the implant remained stable with no further revision. On the axial views we found a 5° lateral tilt of patella in two cases. No significant displacement of the patella was observed.
4. Discussion Several methods have been described to treat patellar bone deficiency during primary or revision total knee arthroplasty [1–5]. Treatment depends on the quality of the remaining bone stock including cemented patellar component, retention of the remaining thin patellar shell, patellar bone grafting [3], gull-wing sagittal patellar osteotomy [4], rebar technique[5]. Trabecular metal patella represents a further therapeutics option that we have used since 2003. TM is a porous tantalum biomaterial developed with a high volumetric porosity and physical and mechanical properties similar to those of bone [6]. This new material is made by chemical vapour infiltration of pure tantalum metal onto a vitreous carbon substrate. It is an interesting solution because of its favourable bone ingrowth characteristics [6] and direct tendon attachment, as indicated by animal studies [7]. In our experience reliable bony fixation to the trabecular metal was observed in all cases when more than 50% amount of bone remained for biological fixation, despite the quality of residual bone. These data support previously reported data by other authors [8,9,13], with the advantage of a longer follow-up. However, we have to point out a failure associated to migration and loosening of the implant in the
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only case of previous patellectomy, where soft tissue was used for fixation of the TM implant. This complication has been already reported by Ries et al. [13]. In their series the authors observed the constant loosening of the implant within 12 months when the majority of the fixation surface (more than 50%) was composed of soft tissue. Recently, disappointing results have also been reported by Kwong and Desai [14] who treated seven patients with previous patellectomy using both total knee arthroplasty or patello-femoral joint replacement. The reason for discrepancy among animal studies [7] that have shown direct soft tissue ingrowth inside the trabecular metal and clinical experience is unclear. One reason might be the impossibility to allow adequate stability during the healing period as reported by Ries et al. [13]. Other authors [14] advise that patients with multiple operations may have an affected vascularity of the skin around the knee, making wound healing difficult and possibly affecting tissue ingrowth into the augment. The weakness of the study consist in the retrospective evaluation of only 10 patients, however it is an homogeneous study, all patients were operated by the same surgeon and the follow-up supplied is longer than any other in the literature concerning TM in TKA with patella bone deficiency. In conclusion, the mid-term results of patellar resurfacing with a trabecular metal implant suggest that a stable fixation can be achieved when at least 50% of contact between residula patellar bone and TM implant could be achieved, whereas with currently available implants the direct attachment of patellar tendon to trabecular metal is not feasible and loosening is the constant end point. References [1] Barrack RL, Matzkin E, Ingraham R, Hengh G, Rorabeck C. Revision knee arthroplasty with patellar replacement versus bony shell. Clin Orthop 1998;356:139–43. [2] Pagnano MW, Scuderi GR, Insall JN. Patellar component resection in revision and reimplantation TKA. Clin Orthop 1998;356:134–8. [3] Hassen A. Bone-grafting for severe patellar bone loss during revision knee arthroplasty. J Bone J Surg 2001;83A:171–6. [4] Kelly V, Roidis N, Blackburn D. Gull wing sagittal patellar osteotomy in total knee arthroplasty, vol. 1 N°2. Technique in Knee Surg; 2002. p. 106–12. [5] Fisher DA. Rebar technique for revision of the failed patellar component, vol. 3 N°1. Technique in Knee Surg; 2004. p. 60–5. [6] Bobyn J, Stackpool GJ, Hacking SA, Tanzer M, Krygier JJ. Characteristic of bone ingrowth and interface mechanics of a new porous tantalum biomaterial. J Bone J Surg 1999;81((5) B):907–14. [7] Hacking S, Bobyn J, Toh K, Tanzer M, Krygier JJ. Biomed Mater Res 2000;52:631–8. [8] Nelson CL, Lonner JH, Kim J, Lotcke PA. Use of trabecular metal patella for marked patella bone loss during revision knee arthroplasty. J Arthroplasty 2003;18(7) (Suppl 1):37–41. [9] Stulberg SD. Bone loss in revision total knee arthroplasty. Graft options and adjuncts. J Arthroplasty 2001;18(3) (Suppl 1):48–50. [10] Insall JN, Dorr LD, Scott RD, Scott WN: Rational of the Knee Society clinical rating system. Clin Orthop 248: 13–14. [11] Baldini A, Anderson J, Zampetti P, Pavlov H, Sculco TA. New patellofemoral scoring system for total arthroplasty. Clin Orthop 2006;452:150–4. [12] Gomes L, Bechtold J, Gustilo R. Patellar prosthesis positioning in total knee arthroplasty: a roentgenographic study. Clin Orthop 1988;236:115–22. [13] Ries M, Cabalo A, Bozic K, Anderson M. Porous tantalum patellar augmentation. The importance of residual bone stock. Clin Orthop 2006;452:166–70. [14] Kwong Y, Desai V. The use of a tantalum-based augmentation of patella in patients with a previous patellectomy. Knee 2008;15:91–4.
