Medical Journal
The Knee –
Minimally invasive Unicondylar Knee Arthroplasty
in a patellectomized patient
Minimally invasive Unicondylar Knee Arthroplasty
in a patellectomized patient
- Gerard Ee
- Hee-Nee Pang
- Ngai-Nung Lo
- Seng-Jin Yeo
Received: 29 September 2011 / Accepted: 11 November 2011 / Published online: 20 November 2011
Springer-Verlag 2011
Key finding
This case study shows that a partial knee replacement (UKA) using a minimally invasive approach can work well for patients who had their kneecap removed in the past. After five years, the patient had no pain, walked normally, and regained strength without knee instability. This suggests UKA may be a good option when only one part of the knee is damaged.
Abstract:
Patellectomized patients may have less satisfactory clinical outcomes following total knee arthroplasty due to decreased extensor mechanism efficiency and potential instability. The literature reports only three case series of patients with prior patellectomy undergoing Unicondylar Knee Arthroplasty (UKA), with mixed results. A minimally invasive fixed-bearing UKA was performed in a patellectomized patient, showing excellent postoperative knee stability and clinical outcomes after five years. Minimally invasive UKA may be a viable option for patellectomized patients with isolated medial compartment osteoarthritis and no preoperative extensor deficiency or instability.
Level of evidence: IV.
Keywords
- Patellectomy
- Patella
- Unicondylar
- Knee
- Arthroplasty
- Minimally invasive
Introduction:
The patella plays a vital role in quadriceps efficiency by increasing the moment arm of the extensor mechanism. It also contributes to anterior-posterior stability of the knee by providing a posteriorly directed force to counteract the pull of the hamstrings. Patients often experience quadriceps weakness and extensor lag after a patellectomy, and as a result, patellectomized patients undergoing total knee arthroplasty (TKA) tend to have less predictable results with lower postoperative clinical scores. While there is some literature describing the use of various types of total knee prostheses in patellectomized patients, few authors have reported results of Unicondylar Knee Arthroplasty (UKA) in this population, and none have included objective data on quadriceps strength following UKA.
Case report: A 55-year-old female retired cleaner presented to the clinic with complaints of right knee pain localized to the medial aspect. She did not report any anterior knee pain. She had undergone a right patellectomy for a comminuted patellar fracture 10 years prior, but her current symptoms began approximately three years ago. Her condition had progressively worsened, limiting her ability to walk and making it difficult to climb even one flight of stairs. Conservative treatment had failed, and she was forced to stop working.
Clinical examination revealed a transverse surgical scar on her right knee and a varus knee alignment of 5 degrees. Her active range of motion (ROM) was from 5 to 120 degrees. There was no collateral ligament laxity, and both the Anterior Drawer and Lachman tests were negative. There was no posterior sag and no extension lag, but medial joint line tenderness was noted. Isokinetic testing using Cybex showed peak torque moments of 69 NM, 90 NM, and 136 NM at 30, 60, and 90 degrees of flexion, respectively. KT-1000 testing revealed 5 mm of anterior tibial translation with 89 N of force at 75 degrees of flexion. Her body mass index (BMI) was 25. Plain radiographs demonstrated moderate medial-compartmental osteoarthritis.
An anterior midline skin incision, perpendicular to the previous patellectomy scar, was used, followed by a subvastus approach. All other ligaments, including the trochlea, were found to be normal. After achieving balanced gaps and neutral mechanical alignment, a unicondylar fixed-bearing knee prosthesis (ZUK, Zimmer, Warsaw, IN) was cemented in place. The knee was mobilized immediately postoperatively using a continuous passive motion device. Assisted ambulation began on the first postoperative day, and the patient was discharged on the third postoperative day. Her recovery was uneventful, and by eight weeks post-surgery, she had regained satisfactory ambulatory status.
She has now been followed up for five years since the index surgery. She does not report anterior knee pain or any symptoms of instability. Her knee range of motion is 0 to 147 degrees, and she can walk unaided on level ground and stairs. Most of her quadriceps strength has returned, with torque moments of 65 NM, 89 NM, and 130 NM at 30, 60, and 90 degrees of flexion, respectively, on Cybex testing. KT-1000 testing at 25 degrees of knee flexion showed 5 mm of anterior tibial translation, with no evidence of medio-lateral instability. Postoperative radiographs at five years demonstrated a well-fixed implant in good position, with a neutral mechanical axis and no signs of lateral compartment osteoarthritis.
Discussion: The most important finding of the study was the good quadriceps strength and clinical outcomes in a patellectomized patient five years after undergoing a minimally invasive unicondylar knee arthroplasty (MIS UKA). This case report demonstrated the potential role of UKA in patellectomized patients with isolated medial compartment disease and no signs of knee instability.
A patellectomy compromises the anterior-posterior stability of the knee by disrupting the four-bar linkage formed by the quadriceps, patellar tendon, and the anterior and posterior cruciate ligaments. To compensate for this, several studies have advocated the use of bone autografts from the iliac crest, resected tibial plateau surfaces, or femoral condyles, as well as the use of allografts, in patellar reconstruction to restore the moment arm and improve quadriceps function. However, due to the compromised quadriceps mechanism in such cases, some studies have discouraged any form of arthroplasty in patellectomized knees.
A literature search using the keywords “arthroplasty patellectomy” on PubMed found only three case series describing the use of UKA in patellectomized patients. Marmor reported good results using the Marmor prosthesis in two patients with isolated medial compartment osteoarthritis with an average follow-up of nine years. Insall… (Note: content appears to be truncated and may continue in the original source.)
Walker found that patellectomy had little impact on the outcome. However, Capra and Fehring reported revision of all three Marmor unicondylar prostheses in their patellectomized patients. Two of these failed due to progression of lateral compartment disease, and the third had no discernible reason for failure. Therefore, they advised caution when considering unicompartmental arthroplasty in patients with prior patellectomy. Since quadriceps torque decreases significantly after patellectomy, the minimally invasive technique helps by sparing the quadriceps mechanism and preserving both cruciate ligaments and major capsular structures of the knee.
This results in more natural knee kinematics compared to total knee arthroplasty (TKA), which is especially important given the biomechanical changes from the previous patellectomy.
Although quadriceps-sparing minimally invasive TKA options are available, the MIS UKA technique allows for less soft tissue disruption while better preserving native knee kinematics. Additional benefits of UKA include earlier postoperative range of motion, faster ambulation, shorter hospital stays, and a reduced rehabilitation period. However, meticulous soft tissue balancing is essential, and care must be taken to avoid overloading the lateral compartment. Overall, UKA is a feasible option in patellectomized patients, as it maintains ligament integrity in both sagittal and frontal planes without altering knee kinematics, while offering faster rehabilitation and better preservation of the knee’s four-bar linkage mechanism when compared to conventional TKA.
This case report does have limitations. First, it describes only a single patient, and a larger case series would provide stronger evidence for the benefits of a minimally invasive UKA approach in patellectomized individuals. Second, a longer follow-up period would help assess the risk of arthritis progression. Lastly, the implant used was a unicondylar fixed-bearing prosthesis from Zimmer, and caution should be used in generalizing these results to other implant types.
Despite these limitations, the study demonstrates the feasibility and potential benefits of UKA in a patellectomized patient with isolated medial compartment osteoarthritis and no signs of extensor lag or knee instability after five years of follow-up.
Conflict of interest One author is a paid consultant for Zimmer,
Warsaw, Indiana, US and one author is a paid consultant for Depuy
Orthopaedic International, Leeds, UK.
References
1. Buechel FF (1991) Patellar tendon bone grafting for patellectomized
patients having total knee arthroplasty. Clin Orthop Relat
Res 271:72–78
2. Busfield BT, Ries MD (2006) Whole patellar allograft for total
knee arthroplasty after previous patellectomy. Clin Orthop Relat
Res 450:145–149
3. Cameron HU, Fedorkow DM (1982) The patella in total knee
arthroplasty. Clin Orthop Relat Res 165:197–199
4. Capra SW Jr, Fehring TK (1992) Unicondylar arthroplasty.
A survivorship analysis. J Arthroplast 7(3):247–251
5. Chang MA, Rand JA, Trousdale RT (2005) Patellectomy after
total knee arthroplasty. Clin Orthop Relat Res 440:175–177
6. Dennis D, Komistek R, Scuderi G (2001) In vivo three-dimensional
determination of kinematics for subjects with a normal
knee or a unicompartmental or total knee replacement. J Bone Jt
Surg Am 83-A(Suppl 2 Pt 2):104–115
7. Duthon VB, Fritschy D (2011) Knee extensor mechanism ruptures.
Rev Med Suisse 7(304):1544–1548
8. Goodfellow JW, Kershaw CJ, Benson MK, O’Connor JJ (1988)
The Oxford Knee for unicompartmental osteoarthritis. The first
103 cases. J Bone Jt Surg Br 70(5):692–701
9. Insall J, Aglietti P (1980) A five to seven year follow-up of
unicondylar arthroplasty. J Bone Jt Surg Am 62(8):1329–1337
10. Insall J, Walker P (1976) Unicondylar knee replacement. Clin
Orthop Relat Res 120:83–85
11. Insall JN, Ranawat CS, Aglietti P, Shine J (1976) A comparison
of four models of total knee-replacement prostheses. J Bone Jt
Surg Am 58(6):754–765
12. Kang JD, Papas SN, Rubash HE, McClain EJ Jr (1993) Total
knee arthroplasty in patellectomized patients. J Arthroplast 8(5):
489–501
13. Lakshmanan P, Wilson C (2004) Total knee arthroplasty in a
patellectomised posterior cruciate ligament deficient knee: a new
technique of patellar tendon bone grafting. Knee 11(6):481–484
14. Larson KR, Cracchiolo A III, Dorey FJ, Finerman GA (1991)
Total knee arthroplasty in patients after patellectomy. Clin Orthop
Relat Res 264:243–254
15. Lennox DW, Hungerford DS, Krackow KA (1987) Total knee
arthroplasty following patellectomy. Clin Orthop Relat Res
223:220–224
16. Marmor L (1987) Unicompartmental knee arthroplasty following
patellectomy. Clin Orthop Relat Res 218:164–166
17. Martin SD, Haas SB, Insall JN (1995) Primary total knee
arthroplasty after patellectomy. J Bone Jt Surg Am 77(9):
1323–1330
18. Pang HN, Sathappan SS (2008) Patellar reconstruction using
distal femoral autograft in a patellectomized patient undergoing
total knee arthroplasty. J Arthroplast 23(6):939.e1–939.e7
19. Peeples RS, Margo MK (1978) Function after patellectomy. Clin
Orthop Relat Res 132:180–186
20. Romanowski MR, Repicci JA (2002) Minimally invasive unicondylar
arthroplasty: eight-year-follow-up. JKnee Surg 15(1):17–22
21. Schindler OS, Scott WN (2011) Basic kinematics and biomechanics
of the patello-femoral joint. Part 1: the native patella.
Acta Orthop Belg 77(4):421–431
22. Sledge CB, Ewald FC (1979) Total knee arthroplasty. Experience
at the Robert Breck Brigham Hospital. Clin Orthop Relat Res
145:78–84
23. Tirveilliot F, Migaud H, Tillie B, Vielpeau C, Flautre B, Gougeon
F (2003) Patellar reconstruction during total knee arthroplasty
after previous patellectomy. Rev Chir Orthop Reparatrice Appar
Mot 89(7):613–620
24. Watkins MP, Harris BA, Wender S, Zarins B, Rowe CR (1983)
Effect of patellectomy on the function of quadriceps and hamstrings.
J Bone Jt Surg Am 65(3):390–395
25. Wendt PP, Johnson RP (1985) A study of quadriceps excursion,
torque, and the effect of patellectomy on cadaver knees. J Bone Jt
Surg Am 67(5):726–732