- Email: [email protected]
Update on Patellofemoral Arthroplasty
Update on Patellofemoral Arthroplasty Matthew M. Crowe, MD, and Diane L. Dahm, MD Patellofemoral arthroplasty (PFA) has been used for the treatment of isolated patellofemoral arthritis for more than 30 years. Changes in implant design, patient selection, and technical considerations have led to improved short-term and midterm outcomes over the past decade. These outcomes suggest that PFA is a valuable tool for patients with isolated anterior compartment degenerative arthritis, especially in the setting of trochlear dysplasia. PFA may provide benefits over total knee arthroplasty (TKA) for isolated patellofemoral arthritis owing to its preservation of tibiofemoral mechanics, less-invasive nature, and the possibility of conversion to TKA using primary TKA components. This review discusses the indications for implant design considerations, proper patient selection, and technical considerations made during surgery which have resulted in PFA becoming a more reliable and useful tool in the treatment of anterior knee pain because of degenerative arthritis. Oper Tech Sports Med 23:157-163 C 2015 Published by Elsevier Inc.
KEYWORDS patellofemoral arthroplasty, PFA, patellofemoral arthritis
Introduction
I
solated patellofemoral arthritis remains a relatively uncommon but challenging condition to treat. It is estimated that only approximately 9% of patients older than 40 years presenting with knee pain have radiographic evidence of isolated patellofemoral arthritis.1 Owing to the relatively small prevalence of disease and high revision rates with early prostheses,2-4 patellofemoral arthroplasty (PFA) has remained a controversial option. More recent advances in patient selection, implant design, and attention to implant positioning have led to significantly improved midterm results.5-7 With an increasingly younger and more demanding population seeking treatment, it is anticipated that PFA will provide more predictable and durable results than cartilage restoration options do in middle-aged patients while preserving more of the joint than total knee arthroplasty (TKA) does for the patients of all ages with isolated patellofemoral arthritis.
Prosthetic Design Considerations A number of articles have reviewed the differences between early (first generation) and newer (second generation) PFA Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN. Address reprint requests to Diane L. Dahm, MD, Department of Orthopedic Surgery, Mayo Clinic, 200 First St. SW, Rochester, MN 55905. E-mail: [email protected]
http://dx.doi.org/10.1053/j.otsm.2015.05.001 1060-1872/& 2015 Published by Elsevier Inc.
implants.8-11 First-generation implants were introduced in 1979 and followed the poorly performing Vitallium McKeever patellar button. These used an inlay design where the medial and lateral edges of the prosthesis were designed to blend with the native edges of the trochlea. With this type of design, native anatomy influenced implant positioning. Given the high prevalence of trochlear dysplasia in this population,5 reproducibility was challenging and a tendency to flex the component existed; leading to a high rate of snapping and clunking as the patella transitioned onto and off of the prosthesis in extension.11 Furthermore, these prostheses were more highly constrained with a deeper trochlear groove, theoretically leading to less natural kinematics and higher wear. Outcomes with such implants varied, but studies demonstrated revision or TKA conversion rates as high as 15%-35% in short-term to midterm follow-up.8 Recently, some interest has returned to inlay designs with newer patient-specific implants. These include the Arthrosurface prosthesis that is used for small lesions and the custom, computed tomography (CT)-based Kinamed prosthesis used for complete resurfacing. Both of these designs may be at risk of failure in trochlear dysplasia given their inability to change patellofemoral joint mechanics. Second-generation implants that use an anterior femoral cut similar to that used for TKA have come to the market from multiple manufacturers over the past 2 decades. This onlay design allows for resurfacing of the entire anterior compartment and allows for more correction of a dysplastic trochlea. Many newer designs extend more proximally than older 157
158 designs or native trochlea does, which promotes uniform engagement of the patella at the proximal edge of the prosthesis to reduce clunk and subluxation in extension even with mild patella alta.9 More recent designs are also less constrained and are therefore more forgiving regarding subtle patellofemoral malalignment.7,8 Results with a second-generation implant at our institution at a mean of 4 years showed statistically significant improvements in Knee Society function, pain, and stair-climbing scores as well as Tegner and University of California, Los Angeles activity scores. The revision rate was 2 of 59 (3.4%) at final follow-up, with these patients requiring conversion to TKA for tibiofemoral progression at 50 and 63 months. Multiple other studies have found similar short-term and midterm results with second-generation implants.6,12 We continue to favor use of an onlay-type prosthesis, as the high incidence of trochlear dysplasia makes even newer-style inlay prostheses less predictable.
Clinical Evaluation Similar to tibiofemoral unicompartmental arthroplasty, results improve when strict patient selection criteria are used. PFA is indicated only for isolated, end-stage, unicompartmental patellofemoral arthritis. This is in contrast to all other anterior knee pain for which conservative management has failed. Isolated patellofemoral arthritis is often multifactorial, consisting of genetic, posttraumatic, and dysplastic causes. It is important to rule out tibiofemoral arthritis as well as any possibility of inflammatory arthritis. It is critical to inquire about remote patellar instability, as hypertrophic changes or diminished activity may improve previous instability that could be unmasked with the low-friction bearing surface of a PFA. An ideal patient has complaints of pain and crepitus with stair climbing, long periods of sitting, and walking on uneven surfaces, with less or no difficulty walking on flat surfaces. The physical examination requires a complete evaluation of the lower extremities. Assessing hip to ankle standing alignment is important, as PFA is not indicated in patients with significant varus or valgus deformity. Caution should be exercised in patients with greater than 81 valgus or 51 varus deformities.13 A hip examination in the prone position may demonstrate femoral malrotation or hip osteoarthritis. A complete knee examination with attention to the presence of tibiofemoral pathology should be performed, as pain referable to the tibiofemoral joint is unlikely to be relieved following PFA. Despite this, no study has found meniscal injury or anterior cruciate deficiency to be a contraindication to PFA.8 Patellar laxity, apprehension, tilt, grind, Q angle, and the presence of a J sign should be compared with the contralateral side. Examination signs indicative of instability require a careful evaluation of the underlying cause. Lateral patellar subluxation due to lateral patellofemoral wear in the presence of trochlear dysplasia may be appropriately treated with PFA, whereas angular deformities may require antecedent or combined procedures.14 Regarding body mass index, studies have failed to show increased revision rates at short-term and midterm follow-up5; however, with follow-up of 13.3 years, van
M.M. Crowe, D.L. Dahm Jonbergen et al4 found a significantly increased rate of revision for patients with a body mass index more than 30 kg/m2. The radiographic examination is an extension of the physical examination and history. Full-length standing hip-knee-ankle, standing anteroposterior, posteroanterior flexion, lateral, and Merchant views should be obtained. Films are assessed for evidence of hip arthritis, tibiofemoral arthritis, coronal malalignment at the knee, and ankle or hindfoot valgus. Lateral radiographs are examined for evidence of trochlear dysplasia, as described by DeJour, including the crossover sign, supratrochlear spur, and double contour.15 Multiple studies using second-generation implants show the progression of tibiofemoral arthritis to be less likely in patients with trochlear dysplasia, suggesting that these patients may have the most durable results.5,15,16 Patients without dysplasia are counseled that they are at a higher risk of progression of tibiofemoral arthritis, but that in some cases, PFA may be an appropriate bridging procedure, particularly in physiologically younger patients. Assessment of patellar height is important, as patella baja is generally felt to be a contraindication unless corrected.3 A posteroanterior flexion can be helpful to further evaluate tibiofemoral articulation. Currently, advanced imaging is not a prerequisite for surgical consideration; however, CT can be helpful, particularly in patients with instability, to assess for dysplasia, determine tibial tuberosity trochlear groove (TT-TG) distance, and assess whether tibial tubercle realignment is indicated. Magnetic resonance imaging may be useful to determine the presence of tibiofemoral chondromalacia and TT-posterior cruciate ligament distance in place of TT-TG in those with trochlear dysplasia where a TG is not present. It is noteworthy that caution should be exercised in younger patients with CT or magnetic resonance imaging evidence of patellofemoral chondromalacia, but without frank radiographic joint space narrowing or osteophyte formation, as these patients may have nonarthritic sources of pain and less predictable pain relief following PFA.
TKA vs PFA for Isolated Patellofemoral Arthritis Owing to the somewhat unpredictable results reported for early PFA designs, multiple studies have looked to TKA as a possible superior option for patients with isolated patellofemoral arthritis. Multiple studies of TKA for isolated patellofemoral disease show high midterm survivorship, significant improvements in Knee Society functional and objective scores, and a relatively low incidence of anterior knee pain and instability with or without patellar resurfacing.3,6,17,18 No prospective randomized trial has been performed; however, we retrospectively analyzed and compared all patients over a 3year period who underwent arthroplasty for isolated patellofemoral arthritis. At a mean follow-up of 27-29 months, the groups had similar Knee Society Scores of 89 and 90 for PFA and TKA, respectively; however, PFA patients had significantly higher University of California, Los Angeles scores, lower blood loss, and shorter hospital stays. None of these outcomes were affected by age as an independent variable.19 To date,
Update on patellofemoral arthroplasty there is little evidence comparing PFA and TKA in the areas where PFA has theoretical advantages such as a more natural feel to the knee, a faster recovery, or ability to participate in low-impact sport at a higher level. Despite this lack of data, these theoretical benefits along with the bone-conserving nature of PFA make it appealing in appropriate patients. Furthermore, for significantly younger patients where the patient is likely to outlive the implant, conversion of a PFA to TKA may be accomplished with primary implants vs a more complex revision TKA.
Authors' Technical Tips Despite major technical similarities with resurfacing of the anterior compartment in TKA, PFA remains technically demanding owing to the high incidence of trochlear dysplasia, soft tissue imbalance, and patellar and trochlear wear patterns that make using predefined bony landmarks less reliable.
Analgesia The ideal perioperative regional or local anesthetic for the procedure remains a topic of debate. Traditionally, an indwelling femoral nerve catheter was used with an identical protocol to that used for TKA. The risk of falls in TKA patients undergoing continuous femoral nerve blockade are well documented.20,21 Furthermore, the measurable quadriceps strength deficits noted 6 months after femoral nerve blockade
159 for anterior cruciate ligament reconstruction were concerning, as the quadriceps is a dynamic patellar stabilizer.22 This has led to a transition to adductor canal catheter placement for 48 hours or until dismissal. Adductor canal catheters have shown improvements in ambulatory distance in the early postoperative period for TKA patients when compared with femoral nerve blockade.23 If desired, this can be supplemented or replaced with periarticular “cocktail” blocks as used in TKA.24 Analgesia without significant quadriceps dysfunction may be particularly advantageous for PFA patients.
Exposure Exposure for PFA remains similar to standard knee arthroplasty approaches that may include a subvastus, midvastus, or medial parapatellar approach. Care must be taken to preserve the remainder of the joint including the menisci and intermeniscal ligament. Improved patellar mobilization can be accomplished with release of the anterior fat pad, taking care to remain anterior to the intrameniscal ligament.
Implant Positioning and Rotation We currently use a second-generation component (Avon, Stryker, Mahwah, NJ) for which satisfactory early-term and midterm results have been reported.5 An intramedullary pin is used to center the initial guide and aid in setting the sagittal rotation of the anterior cut, which should be parallel to the
A
B
C
D
Figure 1 Preliminary joint preparation of a second-generation PFA. (A) The guide is placed on the distal aspect of the femoral condyles and sagittal alignment compared with the femoral shaft. Intramedullary pins are placed. (B) Similar to TKA, cut height is adjusted to prevent notching and anterior femoral resection is performed (C). (D) The cut surface is inspected for appropriate rotation. (Color version of figure is available online.)
M.M. Crowe, D.L. Dahm
160 anterior cortex of the distal femur (Fig. 1A). The guide is adjusted to the appropriate height for maximal anterior resection without notching at the proximal margin (Fig. 1B). Special attention is given to the internal-external rotation of the anterior cut, as appropriate rotation is critical for proper patellar tracking and stability. The rotation is compared with the transepicondylar axis as well as the tibial plateau. Although the classic mantra of avoiding internal rotation remains important, excessive external rotation lowers the lateral edge of the trochlea, which may increase the likelihood of instability in some patients. We aim to match or slightly externally rotate the trochlear component relative to the transepicondylar axis (Fig. 1D). The remainder of preparation depends on the specific implant being used but in general requires additional bone resection or milling for the distal flange (Figs. 2 and 3). It is important that the distal extent of the prosthesis does not overhang the notch, which can lead to impingement on the anterior cruciate ligament in extension and cause clunking on active extension. The trochlear component, in most cases, is lateralized as much as possible while still ensuring the appropriate contour distally and avoiding overhang beyond the edge of the lateral femoral condyle (Fig. 4). Excessive valgus positioning of the trochlear component should likewise be avoided, as this may lead to a “catch” when the patellar prosthesis reenters the groove from deep flexion to extension. With careful attention to lateralization and rotation of the prosthesis, some amount of preoperative malalignment can be
corrected. Rarely, a tibial tubercle osteotomy is required at the time of PFA.
Patellar Resurfacing Patellar resurfacing is performed in a similar manner as for TKA with medialization of the patellar component and care to avoid excessive “overstuffing” of the joint. However, in cases of limited patellar bone stock, maintaining a minimum resected thickness of 12 mm helps to prevent patellar fracture, and the 1-2 mm increase in total patellar thickness is well tolerated.25 Consideration should be given to the potential compatibility of the chosen patellar component to a TKA system in case of later conversion to TKA.
Indication for Lateral Release and Lateral Lengthening Although lateral release is often indicated in patellofemoral replacements performed for lateral patellofemoral arthritis, it is less often required for PFA performed for posttraumatic arthritis. A release or lengthening is performed after final component implantation if the patella does not correct to neutral rotation with patellar tilt testing. Lateral release is not likely to improve a significantly unstable or subluxating patella. Towel clips are used to mimic the medial closure during trialing. Implant rotation and positioning as well as tibial tubercle position must be carefully considered in joints that are not completely stable during final trialing.
A
B
C
D
Figure 2 (A) The trial and drill guide is placed and the outline is traced with methylene blue. (B and C) Resection is performed with osteotome and high-speed burr. (D) Resection is repeated until the implant sits flush with the distal femoral condyle. (Color version of figure is available online.)
Update on patellofemoral arthroplasty
A
161
B
Figure 3 (A) After appropriate fit is achieved, lug holes are prepared and the trial is placed. (B) Tracking is assessed after patellar preparation with the trial implant and the use of towel clips to reproduce the medial closure. (Color version of figure is available online.)
Figure 4 Non–weight-bearing postoperative A-P and lateral radiographs of a second-generation implant. AP, anteroposterior.
M.M. Crowe, D.L. Dahm
162
Other Considerations
Conclusions
One often overlooked aspect of any unicompartmental arthroplasty or open articular surgery is maintaining the microscopic viability of the retained cartilage. In a rarely discussed study, Pun et al exposed fresh femoral osteochondral specimens to air for 0, 30, 60, or 120 minutes. Samples were either not rewetted or rewetted every 10 or 20 minutes with lactated Ringer solution. Chondrocyte viability was reduced from control in every group and resulted in 60% viability for 10-minute rewetting, 45% for 20-minute rewetting, and 20% without rewetting.26 This, along with a recent study by Farr et al,27 has led us to specifically focus on rewetting the tibiofemoral joint with saline as frequently as possible during preparation of the trochlea.
Despite a history of somewhat unpredictable results, recent advances in patient selection, surgical techniques, and implant design for PFA have made it a useful and powerful tool for specific patients with isolated end-stage patellofemoral arthritis. More research is necessary to define the long-term outcomes of current implant designs. However, midterm follow-up suggests that PFA is reliable and may have benefits over TKA in younger, more active patients as well as those of any age with advanced arthritis in the setting of trochlear dysplasia. Careful attention to surgical technique and implant positioning is important for optimal results.
References Postoperative Care Postoperative care of PFA patients is similar to that of TKA patients; however, we do restrict full weight-bearing until return of quad function to avoid a flare of pain and inflammation in the native compartments. Early rehabilitation emphasizes swelling control and quadriceps activation with progressive range-of-motion exercises and addition of primarily closed kinetic chain-strengthening exercises when tolerated. Intermittent pain and mild effusions throughout the first 3-6 months are not unusual, and patients must be reminded that they have an arthroplasty and must protect it initially.
Risk of Tibiofemoral Arthritis Progression Progression of tibiofemoral arthritis remains one of the largest concerns with PFA, as PFA loosening is quite rare. Historical series show a conversion rate to TKA of up to 22% at 5- to 15-year follow-up.8 A study of secondgeneration implants at a mean of 7 years shows a 12% conversion rate because of progression of tibiofemoral arthritis. Interestingly, no patients with preoperative trochlear dysplasia required conversion, whereas 17% of patients without trochlear dysplasia required conversion, suggesting that osteoarthritis that is not clearly mechanically related is a risk factor for progression.16 We have previously reviewed 59 patients for radiographic evidence of arthritis at a mean of 4 years and found that 14 of 20 patients without dysplasia showed some tibiofemoral progression at a mean of 4 years, whereas only 5 of 39 patients with dysplasia showed progression. Despite the radiographic progression, only 2 patients required conversion to TKA at 50 and 63 months.5 Although some are hesitant to see any arthroplasty as a bridge to TKA, in some younger patients, PFA may provide an option at an age or activity level when TKA is inappropriate. As long-term results become available, it will be important to carefully inspect outcomes, as some late conversions to TKA may not represent a failure of treatment, but rather a successful bridge to avoid a more serious revision of a TKA.
1. Davies AP, Vince AS, Shepstone C, et al: The radiologic prevalence of patellofemoral osteoarthritis. Clin Orthop Relat Res (402):206-212, 2002 2. Leadbetter WB, Ragland PS, Mont MA: The appropriate use of patellofemoral arthroplasty: An analysis of reported indications, contraindications, and failures. Clin Orthop Relat Res436):91-99, 2005 3. Delanois RE, McGrath MS, Ulrich SD, et al: Results of total knee replacement for isolated patellofemoral arthritis: When not to perform a patellofemoral arthroplasty. Orthop Clin North Am 39(3):381-388, 2008. [vii] 4. van Jonbergen H-PW, Werkman DM, Barnaart LF, et al: Long-term outcomes of patellofemoral arthroplasty. J Arthroplasty 25(7):1066-1071, 2010 5. Dahm DL, Kalisvaart MM, Stuart MJ, et al: Patellofemoral arthroplasty: Outcomes and factors associated with early progression of tibiofemoral arthritis. Knee Surg Sports Traumatol Arthrosc 22(10):2554-2559, 2014 6. Mont MA, Johnson AJ, Naziri Q, et al: Patellofemoral arthroplasty: 7-year mean follow-up. J Arthroplasty 27(3):358-361, 2012 7. Lonner JH, Bloomfield MR: The clinical outcome of patellofemoral arthroplasty. Orthop Clin North Am 44(3):271-280, 2013. [vii] 8. Lustig S: Patellofemoral arthroplasty. Orthop Traumatol 100(suppl 1): S35-S43, 2014 9. Lonner JH: Patellofemoral arthroplasty: The impact of design on outcomes. Orthop Clin North Am 39(3):347-354, 2008. [vi] 10. Lustig S, Magnussen RA, Dahm DL, et al: Patellofemoral arthroplasty, where are we today? Knee Surg Sports Traumatol Arthrosc 20 (7):1216-1226, 2012 11. Lonner JH: Patellofemoral arthroplasty: Pros, cons, and design considerations. Clin Orthop Relat Res (428):158-165, 2004 12. Morris MJ, Lombardi Jr AV, Berend KR, et al: Clinical results of patellofemoral arthroplasty. J Arthroplasty 28(suppl 9):199-201, 2013 13. Walker T, Perkinson B, Mihalko WM: Patellofemoral arthroplasty: The other unicompartmental knee replacement. J Bone Joint Surg Am 94 (18):1712-1720, 2012 14. Arendt EA, Dahm DL, Dejour D, et al: Patellofemoral joint: From instability to arthritis. Instr Course Lect 63:355-368, 2014 15. Tecklenburg K, Dejour D, Hoser C, et al: Bony and cartilaginous anatomy of the patellofemoral joint. Knee Surg Sports Traumatol Arthrosc 14 (3):235-240, 2006 16. Nicol SG, Loveridge JM, Weale AE, et al: Arthritis progression after patellofemoral joint replacement. Knee 13(4):290-295, 2006 17. Mont MA, Haas S, Mullick T, et al: Total knee arthroplasty for patellofemoral arthritis. J Bone Joint Surg Am 84(11):1977-1981, 2002 18. Parvizi J, Stuart MJ, Pagnano MW, et al: Total knee arthroplasty in patients with isolated patellofemoral arthritis. Clin Orthop Relat Res (392): 147-152, 2001 19. Dahm DL, Al-Rayashi W, Dajani K, et al: Patellofemoral arthroplasty versus total knee arthroplasty in patients with isolated patellofemoral osteoarthritis. Am J Orthop 39(10):487-491, 2010 20. Pelt CE, Anderson AW, Anderson MB, et al: Postoperative falls after total knee arthroplasty in patients with a femoral nerve catheter: Can we reduce the incidence? J Arthroplasty 29(6):1154-1157, 2014
Update on patellofemoral arthroplasty 21. Sharma S, Iorio R, Specht LM, et al: Complications of femoral nerve block for total knee arthroplasty. Clin Orthop Relat Res 468(1):135-140, 2010 22. Krych A, Arutyunyan G, Kuzma S, et al: Adverse effect of femoral nerve blockade on quadriceps strength and function after ACL reconstruction. J Knee Surg 28(1):83-88, 2014 23. Mudumbai SC, Kim TE, Howard SK, et al: Continuous adductor canal blocks are superior to continuous femoral nerve blocks in promoting early ambulation after TKA. Clin Orthop Relat Res 472(5):1377-1383, 2014 24. Spangehl MJ, Clarke HD, Hentz JG, et al: The Chitranjan Ranawat Award: Periarticular injections and femoral & sciatic blocks provide similar pain
163 relief after TKA: A randomized clinical trial. Clin Orthop Relat Res 473(1):45-53, 2015 25. Bengs BC, Scott RD: The effect of patellar thickness on intraoperative knee flexion and patellar tracking in total knee arthroplasty. J Arthroplasty 21(5):650-655, 2006 26. Pun SY, Teng MS, Kim HT: Periodic rewetting enhances the viability of chondrocytes in human articular cartilage exposed to air. J Bone Joint Surg Br 88-B(11):1528-1532, 2006 27. Farr J, Matthew LM, Stoker AM, et al: Effects on exposed articular cartilage during open surgical procedures: A comparison of various fluids in an animal model. Arthroscopy 31(1):113-117, 2015
KEYWORDS patellofemoral arthroplasty, PFA, patellofemoral arthritis
Introduction
I
solated patellofemoral arthritis remains a relatively uncommon but challenging condition to treat. It is estimated that only approximately 9% of patients older than 40 years presenting with knee pain have radiographic evidence of isolated patellofemoral arthritis.1 Owing to the relatively small prevalence of disease and high revision rates with early prostheses,2-4 patellofemoral arthroplasty (PFA) has remained a controversial option. More recent advances in patient selection, implant design, and attention to implant positioning have led to significantly improved midterm results.5-7 With an increasingly younger and more demanding population seeking treatment, it is anticipated that PFA will provide more predictable and durable results than cartilage restoration options do in middle-aged patients while preserving more of the joint than total knee arthroplasty (TKA) does for the patients of all ages with isolated patellofemoral arthritis.
Prosthetic Design Considerations A number of articles have reviewed the differences between early (first generation) and newer (second generation) PFA Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN. Address reprint requests to Diane L. Dahm, MD, Department of Orthopedic Surgery, Mayo Clinic, 200 First St. SW, Rochester, MN 55905. E-mail: [email protected]
http://dx.doi.org/10.1053/j.otsm.2015.05.001 1060-1872/& 2015 Published by Elsevier Inc.
implants.8-11 First-generation implants were introduced in 1979 and followed the poorly performing Vitallium McKeever patellar button. These used an inlay design where the medial and lateral edges of the prosthesis were designed to blend with the native edges of the trochlea. With this type of design, native anatomy influenced implant positioning. Given the high prevalence of trochlear dysplasia in this population,5 reproducibility was challenging and a tendency to flex the component existed; leading to a high rate of snapping and clunking as the patella transitioned onto and off of the prosthesis in extension.11 Furthermore, these prostheses were more highly constrained with a deeper trochlear groove, theoretically leading to less natural kinematics and higher wear. Outcomes with such implants varied, but studies demonstrated revision or TKA conversion rates as high as 15%-35% in short-term to midterm follow-up.8 Recently, some interest has returned to inlay designs with newer patient-specific implants. These include the Arthrosurface prosthesis that is used for small lesions and the custom, computed tomography (CT)-based Kinamed prosthesis used for complete resurfacing. Both of these designs may be at risk of failure in trochlear dysplasia given their inability to change patellofemoral joint mechanics. Second-generation implants that use an anterior femoral cut similar to that used for TKA have come to the market from multiple manufacturers over the past 2 decades. This onlay design allows for resurfacing of the entire anterior compartment and allows for more correction of a dysplastic trochlea. Many newer designs extend more proximally than older 157
158 designs or native trochlea does, which promotes uniform engagement of the patella at the proximal edge of the prosthesis to reduce clunk and subluxation in extension even with mild patella alta.9 More recent designs are also less constrained and are therefore more forgiving regarding subtle patellofemoral malalignment.7,8 Results with a second-generation implant at our institution at a mean of 4 years showed statistically significant improvements in Knee Society function, pain, and stair-climbing scores as well as Tegner and University of California, Los Angeles activity scores. The revision rate was 2 of 59 (3.4%) at final follow-up, with these patients requiring conversion to TKA for tibiofemoral progression at 50 and 63 months. Multiple other studies have found similar short-term and midterm results with second-generation implants.6,12 We continue to favor use of an onlay-type prosthesis, as the high incidence of trochlear dysplasia makes even newer-style inlay prostheses less predictable.
Clinical Evaluation Similar to tibiofemoral unicompartmental arthroplasty, results improve when strict patient selection criteria are used. PFA is indicated only for isolated, end-stage, unicompartmental patellofemoral arthritis. This is in contrast to all other anterior knee pain for which conservative management has failed. Isolated patellofemoral arthritis is often multifactorial, consisting of genetic, posttraumatic, and dysplastic causes. It is important to rule out tibiofemoral arthritis as well as any possibility of inflammatory arthritis. It is critical to inquire about remote patellar instability, as hypertrophic changes or diminished activity may improve previous instability that could be unmasked with the low-friction bearing surface of a PFA. An ideal patient has complaints of pain and crepitus with stair climbing, long periods of sitting, and walking on uneven surfaces, with less or no difficulty walking on flat surfaces. The physical examination requires a complete evaluation of the lower extremities. Assessing hip to ankle standing alignment is important, as PFA is not indicated in patients with significant varus or valgus deformity. Caution should be exercised in patients with greater than 81 valgus or 51 varus deformities.13 A hip examination in the prone position may demonstrate femoral malrotation or hip osteoarthritis. A complete knee examination with attention to the presence of tibiofemoral pathology should be performed, as pain referable to the tibiofemoral joint is unlikely to be relieved following PFA. Despite this, no study has found meniscal injury or anterior cruciate deficiency to be a contraindication to PFA.8 Patellar laxity, apprehension, tilt, grind, Q angle, and the presence of a J sign should be compared with the contralateral side. Examination signs indicative of instability require a careful evaluation of the underlying cause. Lateral patellar subluxation due to lateral patellofemoral wear in the presence of trochlear dysplasia may be appropriately treated with PFA, whereas angular deformities may require antecedent or combined procedures.14 Regarding body mass index, studies have failed to show increased revision rates at short-term and midterm follow-up5; however, with follow-up of 13.3 years, van
M.M. Crowe, D.L. Dahm Jonbergen et al4 found a significantly increased rate of revision for patients with a body mass index more than 30 kg/m2. The radiographic examination is an extension of the physical examination and history. Full-length standing hip-knee-ankle, standing anteroposterior, posteroanterior flexion, lateral, and Merchant views should be obtained. Films are assessed for evidence of hip arthritis, tibiofemoral arthritis, coronal malalignment at the knee, and ankle or hindfoot valgus. Lateral radiographs are examined for evidence of trochlear dysplasia, as described by DeJour, including the crossover sign, supratrochlear spur, and double contour.15 Multiple studies using second-generation implants show the progression of tibiofemoral arthritis to be less likely in patients with trochlear dysplasia, suggesting that these patients may have the most durable results.5,15,16 Patients without dysplasia are counseled that they are at a higher risk of progression of tibiofemoral arthritis, but that in some cases, PFA may be an appropriate bridging procedure, particularly in physiologically younger patients. Assessment of patellar height is important, as patella baja is generally felt to be a contraindication unless corrected.3 A posteroanterior flexion can be helpful to further evaluate tibiofemoral articulation. Currently, advanced imaging is not a prerequisite for surgical consideration; however, CT can be helpful, particularly in patients with instability, to assess for dysplasia, determine tibial tuberosity trochlear groove (TT-TG) distance, and assess whether tibial tubercle realignment is indicated. Magnetic resonance imaging may be useful to determine the presence of tibiofemoral chondromalacia and TT-posterior cruciate ligament distance in place of TT-TG in those with trochlear dysplasia where a TG is not present. It is noteworthy that caution should be exercised in younger patients with CT or magnetic resonance imaging evidence of patellofemoral chondromalacia, but without frank radiographic joint space narrowing or osteophyte formation, as these patients may have nonarthritic sources of pain and less predictable pain relief following PFA.
TKA vs PFA for Isolated Patellofemoral Arthritis Owing to the somewhat unpredictable results reported for early PFA designs, multiple studies have looked to TKA as a possible superior option for patients with isolated patellofemoral arthritis. Multiple studies of TKA for isolated patellofemoral disease show high midterm survivorship, significant improvements in Knee Society functional and objective scores, and a relatively low incidence of anterior knee pain and instability with or without patellar resurfacing.3,6,17,18 No prospective randomized trial has been performed; however, we retrospectively analyzed and compared all patients over a 3year period who underwent arthroplasty for isolated patellofemoral arthritis. At a mean follow-up of 27-29 months, the groups had similar Knee Society Scores of 89 and 90 for PFA and TKA, respectively; however, PFA patients had significantly higher University of California, Los Angeles scores, lower blood loss, and shorter hospital stays. None of these outcomes were affected by age as an independent variable.19 To date,
Update on patellofemoral arthroplasty there is little evidence comparing PFA and TKA in the areas where PFA has theoretical advantages such as a more natural feel to the knee, a faster recovery, or ability to participate in low-impact sport at a higher level. Despite this lack of data, these theoretical benefits along with the bone-conserving nature of PFA make it appealing in appropriate patients. Furthermore, for significantly younger patients where the patient is likely to outlive the implant, conversion of a PFA to TKA may be accomplished with primary implants vs a more complex revision TKA.
Authors' Technical Tips Despite major technical similarities with resurfacing of the anterior compartment in TKA, PFA remains technically demanding owing to the high incidence of trochlear dysplasia, soft tissue imbalance, and patellar and trochlear wear patterns that make using predefined bony landmarks less reliable.
Analgesia The ideal perioperative regional or local anesthetic for the procedure remains a topic of debate. Traditionally, an indwelling femoral nerve catheter was used with an identical protocol to that used for TKA. The risk of falls in TKA patients undergoing continuous femoral nerve blockade are well documented.20,21 Furthermore, the measurable quadriceps strength deficits noted 6 months after femoral nerve blockade
159 for anterior cruciate ligament reconstruction were concerning, as the quadriceps is a dynamic patellar stabilizer.22 This has led to a transition to adductor canal catheter placement for 48 hours or until dismissal. Adductor canal catheters have shown improvements in ambulatory distance in the early postoperative period for TKA patients when compared with femoral nerve blockade.23 If desired, this can be supplemented or replaced with periarticular “cocktail” blocks as used in TKA.24 Analgesia without significant quadriceps dysfunction may be particularly advantageous for PFA patients.
Exposure Exposure for PFA remains similar to standard knee arthroplasty approaches that may include a subvastus, midvastus, or medial parapatellar approach. Care must be taken to preserve the remainder of the joint including the menisci and intermeniscal ligament. Improved patellar mobilization can be accomplished with release of the anterior fat pad, taking care to remain anterior to the intrameniscal ligament.
Implant Positioning and Rotation We currently use a second-generation component (Avon, Stryker, Mahwah, NJ) for which satisfactory early-term and midterm results have been reported.5 An intramedullary pin is used to center the initial guide and aid in setting the sagittal rotation of the anterior cut, which should be parallel to the
A
B
C
D
Figure 1 Preliminary joint preparation of a second-generation PFA. (A) The guide is placed on the distal aspect of the femoral condyles and sagittal alignment compared with the femoral shaft. Intramedullary pins are placed. (B) Similar to TKA, cut height is adjusted to prevent notching and anterior femoral resection is performed (C). (D) The cut surface is inspected for appropriate rotation. (Color version of figure is available online.)
M.M. Crowe, D.L. Dahm
160 anterior cortex of the distal femur (Fig. 1A). The guide is adjusted to the appropriate height for maximal anterior resection without notching at the proximal margin (Fig. 1B). Special attention is given to the internal-external rotation of the anterior cut, as appropriate rotation is critical for proper patellar tracking and stability. The rotation is compared with the transepicondylar axis as well as the tibial plateau. Although the classic mantra of avoiding internal rotation remains important, excessive external rotation lowers the lateral edge of the trochlea, which may increase the likelihood of instability in some patients. We aim to match or slightly externally rotate the trochlear component relative to the transepicondylar axis (Fig. 1D). The remainder of preparation depends on the specific implant being used but in general requires additional bone resection or milling for the distal flange (Figs. 2 and 3). It is important that the distal extent of the prosthesis does not overhang the notch, which can lead to impingement on the anterior cruciate ligament in extension and cause clunking on active extension. The trochlear component, in most cases, is lateralized as much as possible while still ensuring the appropriate contour distally and avoiding overhang beyond the edge of the lateral femoral condyle (Fig. 4). Excessive valgus positioning of the trochlear component should likewise be avoided, as this may lead to a “catch” when the patellar prosthesis reenters the groove from deep flexion to extension. With careful attention to lateralization and rotation of the prosthesis, some amount of preoperative malalignment can be
corrected. Rarely, a tibial tubercle osteotomy is required at the time of PFA.
Patellar Resurfacing Patellar resurfacing is performed in a similar manner as for TKA with medialization of the patellar component and care to avoid excessive “overstuffing” of the joint. However, in cases of limited patellar bone stock, maintaining a minimum resected thickness of 12 mm helps to prevent patellar fracture, and the 1-2 mm increase in total patellar thickness is well tolerated.25 Consideration should be given to the potential compatibility of the chosen patellar component to a TKA system in case of later conversion to TKA.
Indication for Lateral Release and Lateral Lengthening Although lateral release is often indicated in patellofemoral replacements performed for lateral patellofemoral arthritis, it is less often required for PFA performed for posttraumatic arthritis. A release or lengthening is performed after final component implantation if the patella does not correct to neutral rotation with patellar tilt testing. Lateral release is not likely to improve a significantly unstable or subluxating patella. Towel clips are used to mimic the medial closure during trialing. Implant rotation and positioning as well as tibial tubercle position must be carefully considered in joints that are not completely stable during final trialing.
A
B
C
D
Figure 2 (A) The trial and drill guide is placed and the outline is traced with methylene blue. (B and C) Resection is performed with osteotome and high-speed burr. (D) Resection is repeated until the implant sits flush with the distal femoral condyle. (Color version of figure is available online.)
Update on patellofemoral arthroplasty
A
161
B
Figure 3 (A) After appropriate fit is achieved, lug holes are prepared and the trial is placed. (B) Tracking is assessed after patellar preparation with the trial implant and the use of towel clips to reproduce the medial closure. (Color version of figure is available online.)
Figure 4 Non–weight-bearing postoperative A-P and lateral radiographs of a second-generation implant. AP, anteroposterior.
M.M. Crowe, D.L. Dahm
162
Other Considerations
Conclusions
One often overlooked aspect of any unicompartmental arthroplasty or open articular surgery is maintaining the microscopic viability of the retained cartilage. In a rarely discussed study, Pun et al exposed fresh femoral osteochondral specimens to air for 0, 30, 60, or 120 minutes. Samples were either not rewetted or rewetted every 10 or 20 minutes with lactated Ringer solution. Chondrocyte viability was reduced from control in every group and resulted in 60% viability for 10-minute rewetting, 45% for 20-minute rewetting, and 20% without rewetting.26 This, along with a recent study by Farr et al,27 has led us to specifically focus on rewetting the tibiofemoral joint with saline as frequently as possible during preparation of the trochlea.
Despite a history of somewhat unpredictable results, recent advances in patient selection, surgical techniques, and implant design for PFA have made it a useful and powerful tool for specific patients with isolated end-stage patellofemoral arthritis. More research is necessary to define the long-term outcomes of current implant designs. However, midterm follow-up suggests that PFA is reliable and may have benefits over TKA in younger, more active patients as well as those of any age with advanced arthritis in the setting of trochlear dysplasia. Careful attention to surgical technique and implant positioning is important for optimal results.
References Postoperative Care Postoperative care of PFA patients is similar to that of TKA patients; however, we do restrict full weight-bearing until return of quad function to avoid a flare of pain and inflammation in the native compartments. Early rehabilitation emphasizes swelling control and quadriceps activation with progressive range-of-motion exercises and addition of primarily closed kinetic chain-strengthening exercises when tolerated. Intermittent pain and mild effusions throughout the first 3-6 months are not unusual, and patients must be reminded that they have an arthroplasty and must protect it initially.
Risk of Tibiofemoral Arthritis Progression Progression of tibiofemoral arthritis remains one of the largest concerns with PFA, as PFA loosening is quite rare. Historical series show a conversion rate to TKA of up to 22% at 5- to 15-year follow-up.8 A study of secondgeneration implants at a mean of 7 years shows a 12% conversion rate because of progression of tibiofemoral arthritis. Interestingly, no patients with preoperative trochlear dysplasia required conversion, whereas 17% of patients without trochlear dysplasia required conversion, suggesting that osteoarthritis that is not clearly mechanically related is a risk factor for progression.16 We have previously reviewed 59 patients for radiographic evidence of arthritis at a mean of 4 years and found that 14 of 20 patients without dysplasia showed some tibiofemoral progression at a mean of 4 years, whereas only 5 of 39 patients with dysplasia showed progression. Despite the radiographic progression, only 2 patients required conversion to TKA at 50 and 63 months.5 Although some are hesitant to see any arthroplasty as a bridge to TKA, in some younger patients, PFA may provide an option at an age or activity level when TKA is inappropriate. As long-term results become available, it will be important to carefully inspect outcomes, as some late conversions to TKA may not represent a failure of treatment, but rather a successful bridge to avoid a more serious revision of a TKA.
1. Davies AP, Vince AS, Shepstone C, et al: The radiologic prevalence of patellofemoral osteoarthritis. Clin Orthop Relat Res (402):206-212, 2002 2. Leadbetter WB, Ragland PS, Mont MA: The appropriate use of patellofemoral arthroplasty: An analysis of reported indications, contraindications, and failures. Clin Orthop Relat Res436):91-99, 2005 3. Delanois RE, McGrath MS, Ulrich SD, et al: Results of total knee replacement for isolated patellofemoral arthritis: When not to perform a patellofemoral arthroplasty. Orthop Clin North Am 39(3):381-388, 2008. [vii] 4. van Jonbergen H-PW, Werkman DM, Barnaart LF, et al: Long-term outcomes of patellofemoral arthroplasty. J Arthroplasty 25(7):1066-1071, 2010 5. Dahm DL, Kalisvaart MM, Stuart MJ, et al: Patellofemoral arthroplasty: Outcomes and factors associated with early progression of tibiofemoral arthritis. Knee Surg Sports Traumatol Arthrosc 22(10):2554-2559, 2014 6. Mont MA, Johnson AJ, Naziri Q, et al: Patellofemoral arthroplasty: 7-year mean follow-up. J Arthroplasty 27(3):358-361, 2012 7. Lonner JH, Bloomfield MR: The clinical outcome of patellofemoral arthroplasty. Orthop Clin North Am 44(3):271-280, 2013. [vii] 8. Lustig S: Patellofemoral arthroplasty. Orthop Traumatol 100(suppl 1): S35-S43, 2014 9. Lonner JH: Patellofemoral arthroplasty: The impact of design on outcomes. Orthop Clin North Am 39(3):347-354, 2008. [vi] 10. Lustig S, Magnussen RA, Dahm DL, et al: Patellofemoral arthroplasty, where are we today? Knee Surg Sports Traumatol Arthrosc 20 (7):1216-1226, 2012 11. Lonner JH: Patellofemoral arthroplasty: Pros, cons, and design considerations. Clin Orthop Relat Res (428):158-165, 2004 12. Morris MJ, Lombardi Jr AV, Berend KR, et al: Clinical results of patellofemoral arthroplasty. J Arthroplasty 28(suppl 9):199-201, 2013 13. Walker T, Perkinson B, Mihalko WM: Patellofemoral arthroplasty: The other unicompartmental knee replacement. J Bone Joint Surg Am 94 (18):1712-1720, 2012 14. Arendt EA, Dahm DL, Dejour D, et al: Patellofemoral joint: From instability to arthritis. Instr Course Lect 63:355-368, 2014 15. Tecklenburg K, Dejour D, Hoser C, et al: Bony and cartilaginous anatomy of the patellofemoral joint. Knee Surg Sports Traumatol Arthrosc 14 (3):235-240, 2006 16. Nicol SG, Loveridge JM, Weale AE, et al: Arthritis progression after patellofemoral joint replacement. Knee 13(4):290-295, 2006 17. Mont MA, Haas S, Mullick T, et al: Total knee arthroplasty for patellofemoral arthritis. J Bone Joint Surg Am 84(11):1977-1981, 2002 18. Parvizi J, Stuart MJ, Pagnano MW, et al: Total knee arthroplasty in patients with isolated patellofemoral arthritis. Clin Orthop Relat Res (392): 147-152, 2001 19. Dahm DL, Al-Rayashi W, Dajani K, et al: Patellofemoral arthroplasty versus total knee arthroplasty in patients with isolated patellofemoral osteoarthritis. Am J Orthop 39(10):487-491, 2010 20. Pelt CE, Anderson AW, Anderson MB, et al: Postoperative falls after total knee arthroplasty in patients with a femoral nerve catheter: Can we reduce the incidence? J Arthroplasty 29(6):1154-1157, 2014
Update on patellofemoral arthroplasty 21. Sharma S, Iorio R, Specht LM, et al: Complications of femoral nerve block for total knee arthroplasty. Clin Orthop Relat Res 468(1):135-140, 2010 22. Krych A, Arutyunyan G, Kuzma S, et al: Adverse effect of femoral nerve blockade on quadriceps strength and function after ACL reconstruction. J Knee Surg 28(1):83-88, 2014 23. Mudumbai SC, Kim TE, Howard SK, et al: Continuous adductor canal blocks are superior to continuous femoral nerve blocks in promoting early ambulation after TKA. Clin Orthop Relat Res 472(5):1377-1383, 2014 24. Spangehl MJ, Clarke HD, Hentz JG, et al: The Chitranjan Ranawat Award: Periarticular injections and femoral & sciatic blocks provide similar pain
163 relief after TKA: A randomized clinical trial. Clin Orthop Relat Res 473(1):45-53, 2015 25. Bengs BC, Scott RD: The effect of patellar thickness on intraoperative knee flexion and patellar tracking in total knee arthroplasty. J Arthroplasty 21(5):650-655, 2006 26. Pun SY, Teng MS, Kim HT: Periodic rewetting enhances the viability of chondrocytes in human articular cartilage exposed to air. J Bone Joint Surg Br 88-B(11):1528-1532, 2006 27. Farr J, Matthew LM, Stoker AM, et al: Effects on exposed articular cartilage during open surgical procedures: A comparison of various fluids in an animal model. Arthroscopy 31(1):113-117, 2015