Unicompartmental Knee Arthritis: Total Knee Arthroplasty

Eric R. Bohm, BEng, M.D., MSc, FRCSC
Assistant Professor
University of Manitoba Joint Replacement Group
Winnipeg, MB

Introduction
Total knee arthroplasty (TKA) is indicated for the management of symptomatic knee arthritis when nonoperative management has failed and the well-informed patient feels that the potential benefits outweigh the risks. While many consider TKA to be the arthroplasty standard of care when there are significant arthritic changes involving two or more compartments, the recent resurgence of interest in patellofemoral arthroplasty and unicompartmental arthroplasty has given the patient and surgeon more options to choose from when only one compartment is involved. Patient satisfaction following knee replacement surgery is related primarily to relief of pain and restoration of function; the other important consideration of course is durability, since the results of revision surgery rarely match those of the primary surgery1. When considering surgical options, the surgeon and patient must therefore balance the competing interests of pain relief, functional result and durability.

TKA for Patellofemoral Arthritis

The patient with debilitating patellofemoral (PF) arthritis and a radiographically normal tibio-femoral articulation requiring surgery, seemingly presents a clinical conundrum: resurface just the diseased compartment using a patellofemoral arthroplasty (PFA), or replace the entire joint with a TKA? The first option is certainly appealing, as it appears more conservative. However, patellofemoral arthroplasty has a spotty track record at best, with survival rates as low as 58% at 16 years in relatively large series. Interestingly the most common reason for revision to TKA is the development of arthritis in the tibio-femoral articulation2. Pain and functional outcomes of patients treated with TKA for isolated patellofemoral arthritis appear good, with multiple authors reporting significant improvement following surgery3-5. These clinical improvements, combined with the documented longevity for TKA of >90% at 15 years6, make TKA a good choice when surgical management of PF arthritis is undertaken.

TKA for Lateral Compartment Arthritis
Surgical management of lateral compartment degeneration can be complicated by the many factors associated with arthritis in this location: rheumatoid arthritis (RA), significant flexion contracture, fixed valgus deformity, attenuation of the medial collateral ligament (MCL) and young age. Most of these factors are considered to be at least relative contra-indications to unicompartmental knee arthroplasty (UKA)7, whereas the results of TKA for RA is impressive, with survivorship of about 90% at 15 years8.

The use of TKA allows the surgeon to deal with both deformities and ligamentous problems in a relative straightforward fashion. Flexion contractures can be corrected by removing extra bone from the distal femur, normal coronal alignment can be restored with accurate distal femur and proximal tibia cuts along with appropriate lateral soft tissue release, and MCL attenuation can be managed with the use of hinged components. Before undertaking these cases, it is important that the surgeon has access to and be familiar with a TKA system that can provide this sort of intra-operative flexibility.

TKA for Medial Compartment Arthritis
The medial compartment of the knee is the most common location of degenerative changes, and accordingly provides the surgeon and patient with the largest number of surgical treatment options: high tibial osteotomy (HTO), UKA or TKA. About 50% of HTOs are revised to TKA by 10 years9, 10% of UKAs are revised to TKA by 10 years6, and 5% of TKAs are revised by 10 years6. It is difficult to directly compare the functional outcomes of HTO to TKA due to a paucity of comparative studies10. However, UKA patients tend to have slightly higher satisfaction rates following surgery than do TKA patients1. When long term durability is the main concern of both the surgeon and patient, TKA provides the most predictable results.

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Conclusion
Patients and surgeons have several options when pursuing surgical management of unicompartmental knee arthritis. While unicompartmental arthroplasty or osteotomy may be theoretically attractive, when objectively balancing the three surgical goals of functional improvement, pain relief and durability, their results have yet to reliably surpass those of TKA.

References

  1. Robertsson, O., et al., Patient satisfaction after knee arthroplasty: a report on 27,372 knees operated on between 1981 and 1995 in Sweden. Acta Orthop Scand, 2000. 71(3): p. 262-7.
  2. Argenson, J.N., et al., Patellofemoral arthroplasty: an update. Clin Orthop Relat Res, 2005. 440: p. 50-3.
  3. Mont, M.A., et al., Total knee arthroplasty for patellofemoral arthritis. J Bone Joint Surg Am, 2002. 84-A(11): p. 1977-81.
  4. Meding, J.B., et al., Total knee arthroplasty for isolated patellofemoral arthritis in younger patients. Clin Orthop Relat Res, 2007. 464: p. 78-82.
  5. Parvizi, J., et al., Total knee arthroplasty in patients with isolated patellofemoral arthritis. Clin Orthop Relat Res, 2001(392): p. 147-52.
  6. The Swedish Knee Arthroplasty Register - Annual Report 2007. 2007, Dep't of Orthopedics, Lund University Hospital.
  7. Laskin, R.S., Unicompartmental knee replacement: some unanswered questions. Clin Orthop Relat Res, 2001(392): p. 267-71.
  8. The Swedish Knee Arthroplasty Register - Annual Report 2006. 2006, Dep't of Orthopedics, Lund University Hospital.
  9. Naudie, D., et al., The Install Award. Survivorship of the high tibial valgus osteotomy. A 10- to -22-year followup study. Clin Orthop Relat Res, 1999(367): p. 18-27.
  10. Brouwer, R.W., et al., Osteotomy for treating knee osteoarthritis. Cochrane Database Syst Rev, 2007(3): p. CD004019.

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