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Total Knee Arthroplasty After Patellectomy
Total Knee Arthroplasty After Patellectomy Michael A. Mont, MD,* Mario John, MD,† Mike S. McGrath, MD,* Peter A. Bonutti, MD,‡ and Michael G. Zywiel, MD* The techniques for total knee arthroplasty in patients who have undergone previous patellectomy are limited in their description. This report briefly reviews the historical and current indications for patellectomy, describes the biomechanics of the patella as well as patella-deficient knees, and presents the techniques and previously reported results for patellar reconstruction at the time of total knee arthroplasty including autograft bone reconstruction, allograft implantation, and the use of a prosthetic patella. While the reported results are limited to a small number of patients, it appears that patellar reconstruction at the time of total knee arthroplasty can provide successful results in appropriately selected patients. Semin Arthro 20:178-182 © 2009 Elsevier Inc. All rights reserved. KEYWORDS total knee replacement, patella, autograft, allograft, functional outcome
T
otal knee arthroplasties have demonstrated high success in alleviating pain and restoring mobility in patients with end-stage degenerative disease. Although techniques for ensuring optimal outcomes are well described, strategies for the management of patients who have undergone a previous patellectomy are less defined. The purpose of this report was to provide a brief overview of the biomechanics of the patella, the history and indications for patellectomy, and an overview of the techniques and reported outcomes of numerous treatment options for patients undergoing total knee arthroplasty after patellectomy.
Indications for Patellectomy Patellectomy has been in use since the mid-19th century for a variety of conditions, ranging from patellar fractures to osteomyelitis. At the start of the 20th century, some orthopedists began strongly condemning the procedure, arguing that the resultant decreased quadriceps muscle strength, loss of protection to the femoral condyles, and unacceptable cosmetic appearance made the procedure highly undesirable.1 Nevertheless, other authors argued that the patella serves no
*Center for Joint Preservation and Reconstruction, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore, Baltimore, MD. †Department of Orthopaedics, Howard University Hospital, Washington, DC. ‡Bonutti Clinic, Effingham, IL. Address reprint requests to Michael A. Mont, MD, the Rubin Institute for Advanced Orthopedics, Center for Joint Preservation and Replacement, Sinai Hospital of Baltimore, 2401 W Belvedere Ave, Baltimore, MD 21215. E-mail: [email protected]; [email protected]
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1045-4527/09/$-see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1053/j.sart.2009.09.010
useful function in the human knee and can be excised without adverse effect.2,3 By the mid-20th century, some authors began to investigate the specific effects of an absent patella on knee joint biomechanics, finding that patellectomy markedly diminished the extension power of the knee.4,5 As the importance of the patella for optimal knee function became better understood, orthopedic surgeons became more reluctant to perform patellectomies, and the indications for the procedure were reduced. In the past few decades, the indications for a total patellectomy have included (1) fractures of the patella not suited to surgical repair, specifically comminuted and widely separated transverse types; (2) infection or neoplastic invasion of the patella; (3) severe painful chondromalacia of the patella; and (4) painful osteoarthritis of the patellofemoral joint. It should be noted that even for the above indications, patellectomy is always a salvage procedure of last resort, when all other options have failed or been judged unsuitable for use. With the recent introduction of patellofemoral arthroplasty prostheses, the contemporary indications are practically limited to complex fractures and uncontrolled infection or tumors. Adult reconstructive surgeons may still occasionally encounter patients who were treated with a total patellectomy.
Biomechanics The patella is a sesamoid bone enclosed within the converging tendons of the 4 extensor muscles of the knee, specifically the vastus medialis, vastus lateralis, vastus intermedius, and rectus femoris muscles. These tendons converge to form the
Total knee arthroplasty after patellectomy patellar tendon, which inserts into the tibial tuberosity below the joint line of the knee. The patella functions as part of a lever and pulley system magnifying and redirecting forces acting across the joint, allowing for more efficient flexion and extension of the knee.6 When the patella is absent, greater extensor mechanism work is required for knee joint motion, especially as the knee approaches full extension.7 In these cases, the strength of extension can be reduced by as much as 20%-70% when compared with a knee with an intact patella.7-9 Even after total knee arthroplasty, this decreased extension strength remains as long as the patella is absent.10 In addition to the increased work of extension, a patellectomy may adversely affect both the stability of the knee and the force transmission vectors across the joint. The patella forms an intrinsic part of the 4-bar linkage system for knee joint stability described by Sledge and Ewald,11 and acts to position the quadriceps muscle and patellar tendon in parallel with the anterior and posterior cruciate ligaments, respectively. When this relationship is disrupted, such as after patellectomy, anterior–posterior instability of the knee can develop, marked by a “plowing” femorotibial motion.12 This motion produces simultaneous compression and anteroposterior translation of the articular surfaces of the joint. Bayne and Cameron13 postulated that chronic knee pain after patellectomy is caused by soft-tissue tension because of anterior displacement of the femoral component. These plowing motions typically lead to erosion of the articular cartilage and rapid progression of generalized knee osteoarthritis. Several authors have reported poor clinical outcomes and high failure rates in patients treated with total knee arthroplasty after patellectomy.10,14,15 This may be the result of altered extensor mechanism function, as well as instability of the post-arthroplasty knee.10,16 Posterior stabilized prosthetic designs seem to provide better clinical outcomes when compared with cruciate-retaining models, with the post-and-cam design preventing anterior displacement of the femur on the tibia during flexion, mitigating the instability associated with an absent patella. Paletta and Laskin17 evaluated the outcomes of total knee arthroplasty in 22 patients postpatellectomy, with 9 patients treated with a posterior-stabilized prosthesis, and the remaining 13 treated with a cruciate-retaining prosthesis. At 5-year follow-up, patients with posterior-stabilized prostheses had significantly higher Knee Society objective scores (89 vs 67 points). Five knees had considerable pain marked by Knee Society pain scores of 30 points or less, all of which had been treated with a cruciate-retaining prostheses. Nevertheless, even with these posterior-stabilized implants, the results in patients with absent patellae appear to be less than optimal, and reconstruction of the patella during knee arthroplasty may be preferred.
Techniques A number of different approaches to functional reconstruction of the patella during knee arthroplasty have been proposed, including autograft reconstruction, allograft implantation, and the use of a prosthetic patella.
179
Autograft Bone Reconstruction Several authors have reported on the use of autograft bone reconstruction of the patella at the time of total knee arthroplasty. Various bone graft donor sites have been proposed, including full-thickness midiliac crest bone graft, resected posteromedial or distal medial condylar bone, as well as resected tibial plateau. Buechel18 additionally suggested the use of fresh-frozen or freeze-dried femoral head or femoral condyle allograft bone if autograft bone is insufficient. Regardless of the source of the graft, the bone is fashioned into an appropriate circular or ovoid shape. If the patient’s patella is intact on the contralateral side, it can be used to size the graft bone. Otherwise, a diameter of approximately 2.5 cm should be appropriate for an average-sized patient. If using iliac crest or tibial plateau bone, the natural eminence of the bone should be positioned to approximate a patellar ridge, and any sharp edges or corners should be trimmed. The nonarticulating surface of the reconstructed patella should be fashioned flat or slightly convex. After the graft has been appropriately shaped, multiple small-diameter fullthickness holes should be drilled into the bone to provide for suture fixation, and to enhance healing to the patient’s patellar tendon. Bone grafting should be performed after the femoral and tibial trial components are in place, to ensure optimal positioning of the reconstructed patella. A pouch is created in the patellar tendon by making a subsynovial incision on the medial aspect of the patellar tendon, at the level of the original patella (or on the lateral aspect if a lateral parapatellar approach was used). The pouch is developed between the synovium and the patellar tendon using blunt dissection. The graft is then placed in the created pouch, and positioned carefully to ensure optimal patellar tracking. Methylene blue dye can be placed on the trochlear groove of the prosthetic femoral component and the knee cycled several times without the graft in place to label (identify) the region of articulation between the extensor mechanism and the distal femur, and to help position the graft. Absorbable sutures are passed starting on the anterior aspect of the patellar tendon, through the full thickness of the graft and the synovium, and back through all the layers using a different drill hole, with knots tied on the anterior aspect of the native tendon to avoid impingement or irritation. Two or 3 sutures should provide sufficient fixation without causing excessive disruption of the patellar tendon blood supply. After cementing the final components in place and confirming proper patellar tracking, retinacular releases and/or reefing can be performed as necessary to eliminate patellar subluxation. The arthrotomy and incision are closed in the typical manner, and standard knee rehabilitation protocols are used, with avoidance of resistive flexion exercises to minimize pressure against the bone graft. Buechel18 used this technique to treat 7 knees in 6 patients. At a mean final follow-up of 75 months (range, 24-125 months), 6 of the 7 knees had good or excellent results, defined as having excellent walking strength, and the ability to ambulate without aids. The final patient developed persis-
180 tent instability after revision arthroplasty and bone graft reconstruction of the patella complicated by reflex sympathetic dystrophy. This patient required the use of a leg brace to prevent knee instability during ambulation at final follow-up. Lakshmanan and Wilson19 used a resected tibial plateau autograft for patellar reconstruction in a single patient who had undergone patellectomy for anterior knee pain 50 years before the index arthroplasty. Nine months after the surgery, the patient had no extensor lag compared with a 30° lag preoperatively; the Knee Society function score of this patient had improved from 40 points to 92 points, and the Knee Society objective knee score was 90 points (preoperative knee score not reported). Pang and Sathappan20 used distal femoral autograft bone to reconstruct the patella at the time of primary total knee arthroplasty in a 55-year-old woman who had undergone patellectomy for a comminuted fracture 10 years earlier. At 24-month follow-up, the Knee Society objective and function scores in this patient had respectively improved from 50 and 40 points preoperatively, to 90 points for both at final follow-up. Her quadriceps muscle strength improved from Medical Research Council grade 4/5 to 5/5, and her total arc range of motion had improved from 85° to 130°, with resolution of a 5° preoperative flexion contracture and no knee pain or instability. These results suggest that the use of bone autograft for patellar reconstruction at the time of total knee arthroplasty can provide excellent short-term outcomes in patients who had a previous patellectomy. Longer follow-up is needed to assess the results of this reconstructive procedure.
Allograft Reconstruction of the Patella Some authors have reported on the use of whole patellar allografts for the treatment of instability and/or progressive extensor lag in patients who underwent total knee arthroplasty and had previously been treated with patellectomy. Busfield and Ries21 described the use of this technique in patients with an intact native extensor mechanism, using a fresh-frozen tendon-patella-tendon allograft sutured to the articular aspect of the native patellar tendon. The graft was prepared by thawing in warm saline and trimming away the tibial tubercle bone if included. The graft articular cartilage can be removed using a blade to reduce immunogenicity. Exposure was obtained using a typical arthrotomy incision, and the graft was placed deep to the native tissue with the distal pole of the donor patella positioned 1 cm proximal to the tibiofemoral joint line, and held in place with several sutures. The knee was then cycled through a full range of motion to ensure proper patellar tracking, and repositioning the graft as necessary. The authors recommended not implanting a patellar button to avoid the possibility of component loosening. The knees were closed in the typical manner, and patients underwent a standard knee rehabilitation protocol. Of 9 knees treated in this manner, 6 patients were considered to have successful results, with mean Knee Society knee and function scores of 85 and 67 points, respectively, at a mean final follow-up of 44 months (range, 39-48 months). Two patients who had preoperative extensor lags of
M.A. Mont et al 35° and 45° were able to perform straight leg raises at the final follow-up. However, mean patellar thickness in the study group decreased from 24 mm at 6 weeks postoperatively, to 15 mm at final follow-up, with partial graft resorption seen in 2 patients. Two patients who failed the procedure developed infections at 5 and 18 months after reconstruction, respectively, and both patients were eventually treated with an above the knee amputation. One patient underwent revision allograft implantation for aseptic graft resorption and fragmentation 1 year postoperatively. At 3-year follow-up, this patient was doing well, with no extensor lag, full range of motion and quadriceps muscle strength, and Knee Society knee and function scores of 100 and 70 points, respectively. Kulkarni et al22 reported a case of a female patient after patellectomy and total knee arthroplasty with progressive extensor lag to a maximum of 50°. Compromise of the extensor mechanism was confirmed intraoperatively, and the patient was treated with allograft reconstruction of the defect. The authors excised the patient’s native extensor mechanism, and used a fresh-frozen extensor allograft, including tibial bone block. The graft was fixed distally to the tibia using cortical screws, and sutured proximally to the quadriceps tendon in a manner that ensured maximal graft tension with the knee in full extension. The authors additionally resurfaced the allograft patella with a prosthetic polyethylene button. The patient’s knee was kept in extension for 4 weeks postoperatively, followed by gradual introduction of knee flexion exercises. At the final follow-up of 3 years, the patient was doing well with a range of motion of 0°-100° and extensor lag of 10°. The patient reported resolution of her previous knee weakness, was able to walk for 30 minutes at a time, and was satisfied with the results of her reconstruction. Radiographic evaluation showed normal patellar tracking, with union of the allograft bone block and the native tibia. Allograft reconstruction of the patella seems to improve quadriceps muscle function and reduce extensor lag. However, there seems to be a considerable risk of complications, notably graft resorption, with this technique, especially in patients treated with a whole patella-tendon graft sutured to the underside of the existing extensor mechanism.
Reconstruction Using a Prosthetic Patella There have been several recent reports concerning the use of a trabecular metal prosthetic implant for patellar reconstruction after total knee arthroplasty.23-25 The ovoid implant has 1 convex surface implanted in contact with the deep aspect of the patellar tendon, and a flat surface on the articular aspect with 3 depressions meant to receive the pegs of a polyethylene articulation surface. The implant is ringed by a number of small holes used to suture the prostheses in place. It can be used in patients with a completely absent patella, as well as in patients who have some remaining patellar bone. A typical arthrotomy is used to expose the knee and the deep aspect of the extensor mechanism. In patients with remaining bone, a hemispherical reamer is used to prepare the patellar fragment to receive the implant. Trial implants are used to guide reaming depth ensuring that appropriate pa-
Total knee arthroplasty after patellectomy tellar height and extensor mechanism tension is restored. In patients with no patella, the level of implantation is determined with the knee in flexion, with a trial implant tacked in place with sutures to ensure proper tracking. After the position is confirmed, the metal base is sutured in place by passing a suture and needle through a fixation hole on the articular aspect of the implant and through the patellar tendon (and predrilled bone fragment, when present), returning to the articular side of the implant through an adjacent fixation hole. The suture is cut at the needle with the ends left loose, and the process is repeated with a new suture through 2 more adjacent fixation holes until sutures have been passed around the entire circumference of the implant. Knots are then tied in a crosswise-fashion proceeding consecutively to opposite sides of the implant, to minimize the chance of implant displacement during fixation. After fixing the metal component, a polyethylene articulating surface is cemented in place. The 3-hole design of the implant accepts components from most knee arthroplasty systems, allowing the use of a surface that matches the existing femoral component. A standard polyethylene component is available for use with the metal implant according to surgeon’s preference. Kwong and Desai23 reported on the use of this technique in 7 patients with previous patellectomy undergoing patellofemoral arthroplasty (4 cases) or total knee arthroplasty (3 cases). At a mean follow-up of 15 months (range, 6-21 months), 3 patients developed implant loosening, 2 had continuing anterior knee pain, and 1 had severely restricted postoperative range of motion that was suspected to be because of the bulk of the implant. The prosthesis was removed in the final patient before the end of the procedure because of an inability to close the wound because of excessive implant bulk. In contrast, Nasser and Poggie24 reported that mean range of motion improved from 62° (range, 10°-110°) to 103° (range, 90°-125°) at a mean follow-up of 32 months (range, 15-49 months) in 11 patients treated with a metal patellar implant for severe bone loss at the time of revision total knee arthroplasty. Mean Knee Society pain and function scores improved from 20 and 24 points preoperatively, to 53 and 69 points, respectively, at final follow-up. The authors further reported that all implants were stable on radiographic evaluation. Ries et al25 proposed that the differences in outcomes using a metal patellar implant in patients after total knee arthroplasty may be related to the degree of patellar bone loss, suggesting that residual bone provides better outcomes. The authors compared clinical outcomes in 7 knees with completely absent bone stock, to those in 11 knees in whom at least 50% of the patellar component was implanted into the host bone. At a minimum 12-month follow-up (range and mean not reported), all 7 patients with no patellar bone stock experienced component loosening, with 2 cases further complicated by extensor mechanism necrosis and rupture. In contrast, 1 patient in the second group experienced component loosening as result of infection, whereas the remaining 10 patients had stable components at final follow-up. Although the use of a metal patella shows promising results in improving extensor mechanism function and reduc-
181 ing anterior knee pain in patients with total knee arthroplasty and deficient patellae, it seems that these results are largely limited to cases in which some patellar bone remains. In patients treated with previous patellectomy, metal patellae seem to present a high risk of component failure necessitating further complicated revision.
Conclusions Patients undergoing primary or revision total knee arthroplasty with previous patellectomy can present a considerable challenge for the arthroplasty surgeon. Because of the altered biomechanics of the knee resulting from loss of the patella, these individuals are at high risk for weaker extensor mechanism function, chronic knee pain, and knee instability, even with the use of posterior-stabilized or highly-constrained implant designs. Although a number of strategies for restoring more natural knee mechanics have been reported, autograft bone reconstruction of the patella seems to have the highest success rates in patients with an otherwise intact extensor mechanism. In patients with compromised quadriceps and/or patellar tendons, allograft reconstruction of the extensor mechanism with distal bone-to-bone fixation should be considered. Although whole-patella allograft reconstruction and metal patella implants both show some promise in reducing pain and restoring function in postpatellectomy knee arthroplasty patients, both techniques seem to have considerable complication rates, and their use should be limited to carefully selected patients. Perhaps because of the relatively low prevalence of patients undergoing total knee arthroplasty after patellectomy, the reported results for all the techniques reviewed in the present article are limited to a small number of patients. We await further reports of the use of these techniques from additional authors to confirm the findings of the present study.
References 1. Heineck AP: The modern operative treatment of fractures of the patella. Surg Gynecol Obstet 9:177, 1909 2. Brooke R: The treatment of fractured patella by excision: A study of morphology and function. Br J Surg 24:733-747, 1937 3. Hey Groves EW: A note on the extension apparatus of the knee joint. Br J Surg 24:747-748, 1937 4. Haxton H: The function of the patella and the effects of its excision. Surg Gynecol Obstet 80:389-395, 1945 5. O’Donoghue DH, Tompkins F, Hays MB: Strength of the quadriceps function after patellectomy. West J Surg 60:159-167, 1952 6. Grelsamer RP, Klein JR: The biomechanics of the patellofemoral joint. J Orthop Sports Phys Ther 28:286-298, 1998 7. Kaufer H: Mechanical function of the patella. J Bone Joint Surg Am 53:1551-1560, 1971 8. Einola S, Aho AJ, Kallio P: Patellectomy after fracture. Long-term follow-up results with special reference to functional disability. Acta Orthop Scand 47:441-447, 1976 9. Lennox IA, Cobb AG, Knowles J, et al: Knee function after patellectomy. A 12- to 48-year follow-up. J Bone Joint Surg Br 76:485-487, 1994 10. Lennox DW, Hungerford DS, Krackow KA: Total knee arthroplasty following patellectomy. Clin Orthop Relat Res 223:220-224, 1987 11. Sledge CB, Ewald FC: Total knee arthroplasty experience at the Robert Breck Brigham Hospital. Clin Orthop Relat Res 145:78-84, 1979 12. Steurer PA Jr, Gradisar IA Jr, Hoyt WA Jr, et al: A clinical study and biomechanical evaluation. Clin Orthop Relat Res 144:84-90, 1979
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182 13. Bayne O, Cameron HU: Total knee arthroplasty following patellectomy. Clin Orthop Relat Res 186:112-114, 1984 14. Joshi AB, Lee CM, Markovic L, et al: Total knee arthroplasty after patellectomy. J Bone Joint Surg Br 76(6):926-929, 1994 15. Larson KR, Cracchiolo A III, Dorey FJ, et al: Total knee arthroplasty in patients after patellectomy. Clin Orthop Relat Res 264:243-254, 1991 16. Cameron HU, Fedorkow DM: The patella in total knee arthroplasty. Clin Orthop Relat Res 165:197-199, 1982 17. Paletta GA Jr, Laskin RS: Total knee arthroplasty after a previous patellectomy. J Bone Joint Surg Am 77:1708-1712, 1995 18. Buechel FF: Patellar tendon bone grafting for patellectomized patients having total knee arthroplasty. Clin Orthop Relat Res 271:72-78, 1991 19. Lakshmanan P, Wilson C: Total knee arthroplasty in a patellectomised posterior cruciate ligament-deficient knee: A new technique of patellar tendon bone grafting. Knee 11:481-484, 2004 20. Pang HN, Sathappan SS: Patellar reconstruction using distal femoral
21. 22.
23. 24. 25.
autograft in a patellectomized patient undergoing total knee arthroplasty. J Arthroplasty 23:e1-e7, 2008 Busfield BT, Ries MD: Whole patellar allograft for total knee arthroplasty after previous patellectomy. Clin Orthop Relat Res 450:145-149, 2006 Kulkarni S, Sawant M, Ireland J: Allograft reconstruction of the extensor mechanism for progressive extensor lag after total knee arthroplasty and previous patellectomy: A 3-year follow-up. J Arthroplasty 14:892894, 1999 Kwong Y, Desai VV: The use of a tantalum-based augmentation patella in patients with a previous patellectomy. Knee 15:91-94, 2008 Nasser S, Poggie RA: Revision and salvage patellar arthroplasty using a porous tantalum implant. J Arthroplasty 19:562-572, 2004 Ries MD, Cabalo A, Bozic KJ, et al: Porous tantalum patellar augmentation: The importance of residual bone stock. Clin Orthop Relat Res 452:166-170, 2006
T
otal knee arthroplasties have demonstrated high success in alleviating pain and restoring mobility in patients with end-stage degenerative disease. Although techniques for ensuring optimal outcomes are well described, strategies for the management of patients who have undergone a previous patellectomy are less defined. The purpose of this report was to provide a brief overview of the biomechanics of the patella, the history and indications for patellectomy, and an overview of the techniques and reported outcomes of numerous treatment options for patients undergoing total knee arthroplasty after patellectomy.
Indications for Patellectomy Patellectomy has been in use since the mid-19th century for a variety of conditions, ranging from patellar fractures to osteomyelitis. At the start of the 20th century, some orthopedists began strongly condemning the procedure, arguing that the resultant decreased quadriceps muscle strength, loss of protection to the femoral condyles, and unacceptable cosmetic appearance made the procedure highly undesirable.1 Nevertheless, other authors argued that the patella serves no
*Center for Joint Preservation and Reconstruction, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore, Baltimore, MD. †Department of Orthopaedics, Howard University Hospital, Washington, DC. ‡Bonutti Clinic, Effingham, IL. Address reprint requests to Michael A. Mont, MD, the Rubin Institute for Advanced Orthopedics, Center for Joint Preservation and Replacement, Sinai Hospital of Baltimore, 2401 W Belvedere Ave, Baltimore, MD 21215. E-mail: [email protected]; [email protected]
178
1045-4527/09/$-see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1053/j.sart.2009.09.010
useful function in the human knee and can be excised without adverse effect.2,3 By the mid-20th century, some authors began to investigate the specific effects of an absent patella on knee joint biomechanics, finding that patellectomy markedly diminished the extension power of the knee.4,5 As the importance of the patella for optimal knee function became better understood, orthopedic surgeons became more reluctant to perform patellectomies, and the indications for the procedure were reduced. In the past few decades, the indications for a total patellectomy have included (1) fractures of the patella not suited to surgical repair, specifically comminuted and widely separated transverse types; (2) infection or neoplastic invasion of the patella; (3) severe painful chondromalacia of the patella; and (4) painful osteoarthritis of the patellofemoral joint. It should be noted that even for the above indications, patellectomy is always a salvage procedure of last resort, when all other options have failed or been judged unsuitable for use. With the recent introduction of patellofemoral arthroplasty prostheses, the contemporary indications are practically limited to complex fractures and uncontrolled infection or tumors. Adult reconstructive surgeons may still occasionally encounter patients who were treated with a total patellectomy.
Biomechanics The patella is a sesamoid bone enclosed within the converging tendons of the 4 extensor muscles of the knee, specifically the vastus medialis, vastus lateralis, vastus intermedius, and rectus femoris muscles. These tendons converge to form the
Total knee arthroplasty after patellectomy patellar tendon, which inserts into the tibial tuberosity below the joint line of the knee. The patella functions as part of a lever and pulley system magnifying and redirecting forces acting across the joint, allowing for more efficient flexion and extension of the knee.6 When the patella is absent, greater extensor mechanism work is required for knee joint motion, especially as the knee approaches full extension.7 In these cases, the strength of extension can be reduced by as much as 20%-70% when compared with a knee with an intact patella.7-9 Even after total knee arthroplasty, this decreased extension strength remains as long as the patella is absent.10 In addition to the increased work of extension, a patellectomy may adversely affect both the stability of the knee and the force transmission vectors across the joint. The patella forms an intrinsic part of the 4-bar linkage system for knee joint stability described by Sledge and Ewald,11 and acts to position the quadriceps muscle and patellar tendon in parallel with the anterior and posterior cruciate ligaments, respectively. When this relationship is disrupted, such as after patellectomy, anterior–posterior instability of the knee can develop, marked by a “plowing” femorotibial motion.12 This motion produces simultaneous compression and anteroposterior translation of the articular surfaces of the joint. Bayne and Cameron13 postulated that chronic knee pain after patellectomy is caused by soft-tissue tension because of anterior displacement of the femoral component. These plowing motions typically lead to erosion of the articular cartilage and rapid progression of generalized knee osteoarthritis. Several authors have reported poor clinical outcomes and high failure rates in patients treated with total knee arthroplasty after patellectomy.10,14,15 This may be the result of altered extensor mechanism function, as well as instability of the post-arthroplasty knee.10,16 Posterior stabilized prosthetic designs seem to provide better clinical outcomes when compared with cruciate-retaining models, with the post-and-cam design preventing anterior displacement of the femur on the tibia during flexion, mitigating the instability associated with an absent patella. Paletta and Laskin17 evaluated the outcomes of total knee arthroplasty in 22 patients postpatellectomy, with 9 patients treated with a posterior-stabilized prosthesis, and the remaining 13 treated with a cruciate-retaining prosthesis. At 5-year follow-up, patients with posterior-stabilized prostheses had significantly higher Knee Society objective scores (89 vs 67 points). Five knees had considerable pain marked by Knee Society pain scores of 30 points or less, all of which had been treated with a cruciate-retaining prostheses. Nevertheless, even with these posterior-stabilized implants, the results in patients with absent patellae appear to be less than optimal, and reconstruction of the patella during knee arthroplasty may be preferred.
Techniques A number of different approaches to functional reconstruction of the patella during knee arthroplasty have been proposed, including autograft reconstruction, allograft implantation, and the use of a prosthetic patella.
179
Autograft Bone Reconstruction Several authors have reported on the use of autograft bone reconstruction of the patella at the time of total knee arthroplasty. Various bone graft donor sites have been proposed, including full-thickness midiliac crest bone graft, resected posteromedial or distal medial condylar bone, as well as resected tibial plateau. Buechel18 additionally suggested the use of fresh-frozen or freeze-dried femoral head or femoral condyle allograft bone if autograft bone is insufficient. Regardless of the source of the graft, the bone is fashioned into an appropriate circular or ovoid shape. If the patient’s patella is intact on the contralateral side, it can be used to size the graft bone. Otherwise, a diameter of approximately 2.5 cm should be appropriate for an average-sized patient. If using iliac crest or tibial plateau bone, the natural eminence of the bone should be positioned to approximate a patellar ridge, and any sharp edges or corners should be trimmed. The nonarticulating surface of the reconstructed patella should be fashioned flat or slightly convex. After the graft has been appropriately shaped, multiple small-diameter fullthickness holes should be drilled into the bone to provide for suture fixation, and to enhance healing to the patient’s patellar tendon. Bone grafting should be performed after the femoral and tibial trial components are in place, to ensure optimal positioning of the reconstructed patella. A pouch is created in the patellar tendon by making a subsynovial incision on the medial aspect of the patellar tendon, at the level of the original patella (or on the lateral aspect if a lateral parapatellar approach was used). The pouch is developed between the synovium and the patellar tendon using blunt dissection. The graft is then placed in the created pouch, and positioned carefully to ensure optimal patellar tracking. Methylene blue dye can be placed on the trochlear groove of the prosthetic femoral component and the knee cycled several times without the graft in place to label (identify) the region of articulation between the extensor mechanism and the distal femur, and to help position the graft. Absorbable sutures are passed starting on the anterior aspect of the patellar tendon, through the full thickness of the graft and the synovium, and back through all the layers using a different drill hole, with knots tied on the anterior aspect of the native tendon to avoid impingement or irritation. Two or 3 sutures should provide sufficient fixation without causing excessive disruption of the patellar tendon blood supply. After cementing the final components in place and confirming proper patellar tracking, retinacular releases and/or reefing can be performed as necessary to eliminate patellar subluxation. The arthrotomy and incision are closed in the typical manner, and standard knee rehabilitation protocols are used, with avoidance of resistive flexion exercises to minimize pressure against the bone graft. Buechel18 used this technique to treat 7 knees in 6 patients. At a mean final follow-up of 75 months (range, 24-125 months), 6 of the 7 knees had good or excellent results, defined as having excellent walking strength, and the ability to ambulate without aids. The final patient developed persis-
180 tent instability after revision arthroplasty and bone graft reconstruction of the patella complicated by reflex sympathetic dystrophy. This patient required the use of a leg brace to prevent knee instability during ambulation at final follow-up. Lakshmanan and Wilson19 used a resected tibial plateau autograft for patellar reconstruction in a single patient who had undergone patellectomy for anterior knee pain 50 years before the index arthroplasty. Nine months after the surgery, the patient had no extensor lag compared with a 30° lag preoperatively; the Knee Society function score of this patient had improved from 40 points to 92 points, and the Knee Society objective knee score was 90 points (preoperative knee score not reported). Pang and Sathappan20 used distal femoral autograft bone to reconstruct the patella at the time of primary total knee arthroplasty in a 55-year-old woman who had undergone patellectomy for a comminuted fracture 10 years earlier. At 24-month follow-up, the Knee Society objective and function scores in this patient had respectively improved from 50 and 40 points preoperatively, to 90 points for both at final follow-up. Her quadriceps muscle strength improved from Medical Research Council grade 4/5 to 5/5, and her total arc range of motion had improved from 85° to 130°, with resolution of a 5° preoperative flexion contracture and no knee pain or instability. These results suggest that the use of bone autograft for patellar reconstruction at the time of total knee arthroplasty can provide excellent short-term outcomes in patients who had a previous patellectomy. Longer follow-up is needed to assess the results of this reconstructive procedure.
Allograft Reconstruction of the Patella Some authors have reported on the use of whole patellar allografts for the treatment of instability and/or progressive extensor lag in patients who underwent total knee arthroplasty and had previously been treated with patellectomy. Busfield and Ries21 described the use of this technique in patients with an intact native extensor mechanism, using a fresh-frozen tendon-patella-tendon allograft sutured to the articular aspect of the native patellar tendon. The graft was prepared by thawing in warm saline and trimming away the tibial tubercle bone if included. The graft articular cartilage can be removed using a blade to reduce immunogenicity. Exposure was obtained using a typical arthrotomy incision, and the graft was placed deep to the native tissue with the distal pole of the donor patella positioned 1 cm proximal to the tibiofemoral joint line, and held in place with several sutures. The knee was then cycled through a full range of motion to ensure proper patellar tracking, and repositioning the graft as necessary. The authors recommended not implanting a patellar button to avoid the possibility of component loosening. The knees were closed in the typical manner, and patients underwent a standard knee rehabilitation protocol. Of 9 knees treated in this manner, 6 patients were considered to have successful results, with mean Knee Society knee and function scores of 85 and 67 points, respectively, at a mean final follow-up of 44 months (range, 39-48 months). Two patients who had preoperative extensor lags of
M.A. Mont et al 35° and 45° were able to perform straight leg raises at the final follow-up. However, mean patellar thickness in the study group decreased from 24 mm at 6 weeks postoperatively, to 15 mm at final follow-up, with partial graft resorption seen in 2 patients. Two patients who failed the procedure developed infections at 5 and 18 months after reconstruction, respectively, and both patients were eventually treated with an above the knee amputation. One patient underwent revision allograft implantation for aseptic graft resorption and fragmentation 1 year postoperatively. At 3-year follow-up, this patient was doing well, with no extensor lag, full range of motion and quadriceps muscle strength, and Knee Society knee and function scores of 100 and 70 points, respectively. Kulkarni et al22 reported a case of a female patient after patellectomy and total knee arthroplasty with progressive extensor lag to a maximum of 50°. Compromise of the extensor mechanism was confirmed intraoperatively, and the patient was treated with allograft reconstruction of the defect. The authors excised the patient’s native extensor mechanism, and used a fresh-frozen extensor allograft, including tibial bone block. The graft was fixed distally to the tibia using cortical screws, and sutured proximally to the quadriceps tendon in a manner that ensured maximal graft tension with the knee in full extension. The authors additionally resurfaced the allograft patella with a prosthetic polyethylene button. The patient’s knee was kept in extension for 4 weeks postoperatively, followed by gradual introduction of knee flexion exercises. At the final follow-up of 3 years, the patient was doing well with a range of motion of 0°-100° and extensor lag of 10°. The patient reported resolution of her previous knee weakness, was able to walk for 30 minutes at a time, and was satisfied with the results of her reconstruction. Radiographic evaluation showed normal patellar tracking, with union of the allograft bone block and the native tibia. Allograft reconstruction of the patella seems to improve quadriceps muscle function and reduce extensor lag. However, there seems to be a considerable risk of complications, notably graft resorption, with this technique, especially in patients treated with a whole patella-tendon graft sutured to the underside of the existing extensor mechanism.
Reconstruction Using a Prosthetic Patella There have been several recent reports concerning the use of a trabecular metal prosthetic implant for patellar reconstruction after total knee arthroplasty.23-25 The ovoid implant has 1 convex surface implanted in contact with the deep aspect of the patellar tendon, and a flat surface on the articular aspect with 3 depressions meant to receive the pegs of a polyethylene articulation surface. The implant is ringed by a number of small holes used to suture the prostheses in place. It can be used in patients with a completely absent patella, as well as in patients who have some remaining patellar bone. A typical arthrotomy is used to expose the knee and the deep aspect of the extensor mechanism. In patients with remaining bone, a hemispherical reamer is used to prepare the patellar fragment to receive the implant. Trial implants are used to guide reaming depth ensuring that appropriate pa-
Total knee arthroplasty after patellectomy tellar height and extensor mechanism tension is restored. In patients with no patella, the level of implantation is determined with the knee in flexion, with a trial implant tacked in place with sutures to ensure proper tracking. After the position is confirmed, the metal base is sutured in place by passing a suture and needle through a fixation hole on the articular aspect of the implant and through the patellar tendon (and predrilled bone fragment, when present), returning to the articular side of the implant through an adjacent fixation hole. The suture is cut at the needle with the ends left loose, and the process is repeated with a new suture through 2 more adjacent fixation holes until sutures have been passed around the entire circumference of the implant. Knots are then tied in a crosswise-fashion proceeding consecutively to opposite sides of the implant, to minimize the chance of implant displacement during fixation. After fixing the metal component, a polyethylene articulating surface is cemented in place. The 3-hole design of the implant accepts components from most knee arthroplasty systems, allowing the use of a surface that matches the existing femoral component. A standard polyethylene component is available for use with the metal implant according to surgeon’s preference. Kwong and Desai23 reported on the use of this technique in 7 patients with previous patellectomy undergoing patellofemoral arthroplasty (4 cases) or total knee arthroplasty (3 cases). At a mean follow-up of 15 months (range, 6-21 months), 3 patients developed implant loosening, 2 had continuing anterior knee pain, and 1 had severely restricted postoperative range of motion that was suspected to be because of the bulk of the implant. The prosthesis was removed in the final patient before the end of the procedure because of an inability to close the wound because of excessive implant bulk. In contrast, Nasser and Poggie24 reported that mean range of motion improved from 62° (range, 10°-110°) to 103° (range, 90°-125°) at a mean follow-up of 32 months (range, 15-49 months) in 11 patients treated with a metal patellar implant for severe bone loss at the time of revision total knee arthroplasty. Mean Knee Society pain and function scores improved from 20 and 24 points preoperatively, to 53 and 69 points, respectively, at final follow-up. The authors further reported that all implants were stable on radiographic evaluation. Ries et al25 proposed that the differences in outcomes using a metal patellar implant in patients after total knee arthroplasty may be related to the degree of patellar bone loss, suggesting that residual bone provides better outcomes. The authors compared clinical outcomes in 7 knees with completely absent bone stock, to those in 11 knees in whom at least 50% of the patellar component was implanted into the host bone. At a minimum 12-month follow-up (range and mean not reported), all 7 patients with no patellar bone stock experienced component loosening, with 2 cases further complicated by extensor mechanism necrosis and rupture. In contrast, 1 patient in the second group experienced component loosening as result of infection, whereas the remaining 10 patients had stable components at final follow-up. Although the use of a metal patella shows promising results in improving extensor mechanism function and reduc-
181 ing anterior knee pain in patients with total knee arthroplasty and deficient patellae, it seems that these results are largely limited to cases in which some patellar bone remains. In patients treated with previous patellectomy, metal patellae seem to present a high risk of component failure necessitating further complicated revision.
Conclusions Patients undergoing primary or revision total knee arthroplasty with previous patellectomy can present a considerable challenge for the arthroplasty surgeon. Because of the altered biomechanics of the knee resulting from loss of the patella, these individuals are at high risk for weaker extensor mechanism function, chronic knee pain, and knee instability, even with the use of posterior-stabilized or highly-constrained implant designs. Although a number of strategies for restoring more natural knee mechanics have been reported, autograft bone reconstruction of the patella seems to have the highest success rates in patients with an otherwise intact extensor mechanism. In patients with compromised quadriceps and/or patellar tendons, allograft reconstruction of the extensor mechanism with distal bone-to-bone fixation should be considered. Although whole-patella allograft reconstruction and metal patella implants both show some promise in reducing pain and restoring function in postpatellectomy knee arthroplasty patients, both techniques seem to have considerable complication rates, and their use should be limited to carefully selected patients. Perhaps because of the relatively low prevalence of patients undergoing total knee arthroplasty after patellectomy, the reported results for all the techniques reviewed in the present article are limited to a small number of patients. We await further reports of the use of these techniques from additional authors to confirm the findings of the present study.
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