To the Editor:

Dr. Hoekman's comments on our article on surgical technique in unicompartmental arthroplasty are appreciated . We were asked to provide an expanded surgical technique for our original paper "Unicompartmental Knee Arthroplasty in Patients Sixty Years of Age or Younger" ( 1 ) This cohort of patients underwent surgery between September 1988 and December 1996 . The instrumentation was not obsolete at that time and Kaplan-Meier analysis revealed a 92 % survivorship at eleven years . As indicated in the authors update, we now use a tibial first MIS ( minimally invasive surgery ) approach.

What Dr. Hoekman characterizes as misinformation is perhaps a misunderstanding of our statement that varus and valgus resection of the distal femur is determined by selecting the appropriate hole on the angle resection guide. This refers to our attempt to resect the distal femur perpendicular to the mechanical axis , when using intramedullary instrumentation , as recommended by others. ( 2-4 ) This should result in a cut parallel to a correct tibial cut. We believe the femoral - tibial cuts should be parallel in flexion and extension and equal in gap . The femoral cut also has a subtle effect of determining the contact point and articulation with the tibial component. We agree with Dr. Hoekman that the end angular alignment , ( varus-valgus ) is determined by the combined implant thickness . The above material can be found in the Zimmer Unicompartmental High Flex Knee manual.

We believe that all medial osteophytes should be removed, and to clarify, while the capsule is subperiosteally elevated, the medial collateral ligament is elevated with a Holman retractor to allow resection. Over-stuffing the joint is to be avoided, and we have noted that the correct tibial size will allow correction, to no greater than five degrees valgus but still allows 2- to 3- mm gap on valgus stress. (5)

We find agreement with many of Dr. Hoekman's observations, including freehand sagittal tibial cuts, shading the femoral component toward the notch to prevent edge loading, and loading the implant slightly more than the uninvolved side.

MIS is certainly more difficult than a standard approach and we hope that our long term MIS results will equal those performed with now obsolete instruments.

John J. Swienckowski D.O.

Donald W. Pennington, D.O.

Corresponding Author: John J. Swienckowski, D.O. Tri-County Orthopedics 281 Grand River, Suite 209 Farmington Hills, MI 48336

References

1-Pennington DW, Swienckowski JJ, Lutes WB, Drake GN: Unicompartmental Knee Arthroplasty in Patients Sixty Years of Age or Younger. J Bone Joint Surg Am.2003;85:1968

2-Tsahakis PJ, Sledge CB, Unicompartmental Knee Arthroplasty, Operative Orthopedics updates, Vol. 1,July/September, Number 1

3-Tria AJ: Minimally Invasive Unicompartmental Knee Arthroplasty, Techniques in Knee Surg Vol. 1, No. 1,Sept. 2002

4-Kozinn SC, Scott R,Current Concepts Review , Unicondylar Knee Arthroplasty , J Bone Joint Surg Am.1989;71:145

5-Swienckowski JJ, Page BJ:Medial Unicompartmental Arthroplasty of the Knee: Use of the L-Cut and and c omparison with the tibial inset method, Clin Orthop, 1989;239:161-7

To the Editor:

Re: Unicompartmental Knee Arthroplasty in Patients Sixty Years of Age and Younger

I am surprised that you would publish this technique article showing obsolete instrumentation. The MIS (minimally invasive surgery) instrumentation for the Miller Galante unicompartmental knee is significantly different and applicable to either a small incision or a standard total knee approach.

Of much greater importance is misinformation regarding the initial femoral cut and its relationship to tibio-femoral alignment. Unlike the “total” knee, the angle of this cut has no bearing on tibio-femoral alignment. Since the uninvolved compartment is not cut or replaced it acts as a pivot point. Alignment is entirely determined by implant thickness of the replaced compartment. A thicker implant in the medial compartment will shift the knee into more valgus, and thinner into less valgus. Conversely, thicker implant in the lateral compartment angles the knee into varus.

Freeing the capsular ligament from the tibia and removal of osteophytes usually allows for a greater thickness of implant to be inserted than bone has been removed. This should be avoided as it is preferable to load the implant more than the uninvolved side. One should avoid, for example, over -stacking the medial compartment with implant so as to align the knee in valgus and instead seek an alignment that loads the implant slightly more than the uninvolved side.

The angle of the initial femoral cut does determine the alignment of the posterior condyle of the femoral component. This can be visualized on the A-P x-ray and compared with the intramedullary axis of the femur since an intramedullary guide is used. Generally I find that 2° is the best fit. Since the posterior condyle is highly rounded, short, and unconstrained, precise alignment of the posterior condyle would not seem to be critical.

As stated in the article, osteophytes should be removed from both the outer margin of the condyle and the intercondylar notch to properly align the femoral cutting guide and implant. The femoral component usually needs to be shaded more toward the notch to avoid edge loading the tibial component.

The now obsolete tibial cutting guide which is shown has a slot for making the sagittal tibial cut. The newer instrumentation has a small groove for guidance. I use neither of these, but align the sagittal saw freehand with the A-P axis of the tibial plateau. This cut should start at the apex of the tibial spine which can be accomplished as the cruciate ligament acts as a buttress to support the saw blade.

I have been doing the Miller-Galante unicompartmental knee for about 15 years and switched to the MIS technique when this instrumentation became available about 3 years ago. Prior to that time I was doing about 4 per year and now am doing 20-30 per year. Doing this operation through a 3-4 inch incision is definitely much more difficult than a standard total knee approach, but the payoff is a much easier postoperative recovery for the patient. If a surgeon is starting this for the first time I would advise doing several with a standard total knee approach and become comfortable with the instrumentation before trying the MIS technique. <

We thank the authors for their knowledgeable insights and appreciate their concerns for the difficult management of young patients with unicompartmental arthrosis.

We agree with their cited literature that patients under 60 years of age with tricompartment disease who have failed conservative measures do reasonably well with total knee arthroplasty(1).

Regarding our patients with unicompartmental disease, high tibial osteotomy was offered to all patients who fit the indications for inclusion in this study. Although a few patients chose high tibial osteotomy, more than 90% opted for unicompartmental knee arthroplasty. We do not view the long term results of high tibial osteotomy as favorable with reports of only 25%excellent results at 11 years(2), patient satisfaction of only 60% at 15 years(3), and 73% good or excellent results at 8 years which declined to 46% at 18 years(4). These less than outstanding results combined with procedure specific risks of high tibial osteotomy such as undercorrection(5) and peroneal nerve palsy(2) make osteotomy a less desirable choice.

Arthroscopic debridement, which, we found,provides temporary relief for many patients, was utilized prior to unicompartmental arthroplasty in selected patients. We also used “biological” alternatives such as osteochondral transfer or microfracture, when we felt the lesion was amenable to these procedures.

In conclusion, we believe that improved surgical technique and component design as well as stringent patient selection should make unicompartmental knee arthroplasty a more viable long-term option.(1, 6)

1. Pennington DW, Swienckowski JJ, Lutes WB, Drake GN. Unicompartmental knee arthroplasty in patients sixty years of age or younger. J Bone Joint Surg. 2003;85A:1968-1973. 2. Marti RK, Verhagen RA, Derdhoffs GM, Moojen TM. Proximal tibial varus osteotomy: indications, technique, and five to twenty-one- year results. J Bone Joint Surg. 2001;83A:164-70. 3. Choi HR, Hasogawa Y, Kondo S, Shimizu T, Ika K, Iwata H. High tibial osteotomy for varus gonarthrosis: a 10- to 24-year follow-up study. J Orthop Sci. 2001;6(6):493-497. 4. Rinonapoli E, Mancini G, Corvaglia A, Musiello S. Tibial osteotomy for varus gonarthrosis: a 10- to 21- year follow-up study. Clin Orthop. 1998;353:185-193. 5. Coventry MB, Llstrup DM, Wallrichs SL. Proximal tibial osteotomy. A critical long-term study of eighty-seven cases. J Bone Joint Surg. 1993; 75A:196-201. 6. Knutson K, Lindstrand A, Lidgren L. Survival of knee arthroplasties. A nationwide multicentre investigation of 8000 cases. J Bone Joint Surg Br. 1986;68:795-803.

Donald Pennington, John Swienckowski, William Lutes and Greg Drake.

To the Editor:

We read “Unicompartmental Knee Arthroplasty in Patients Sixty Years of Age or Younger” by Pennington et al with great interest. The authors demonstrated excellent results at a follow-up of 5.6 to 13.8 years in patients ranging in age from 35 to 60 years. The overall implant survivorship was 92% at a mean of 11 years, despite a substantial prevalence of of radiographic progression (20%) in the unreplaced compartments.

The important issues raised by this report and previous reports of unicompartmental knee arthroplasty are not the excellent results in the first decade of implantation, but rather the substantial decline in outcomes in the second decade of implantation. The results of the current report are not surprising, but rather very much in line with previous reports of unicompartmental knee arthroplasty. The unique difference may be the younger patient population.

We suggest that it may not be appropriate to compare the survivorship results of this series to outstanding results following total knee arthroplasty which continue to be superlative into the second decade and beyond. Font-Rodriguez et al(1) have reported 90.77 % survivorship of total knee arthroplasty at 21 years, Buechel et al.,(2) reported 98% survivorship at 20 years, and Keating et al(3) reported 98.9% survivorship at 15 years. In addition, it is difficult to compare a series of total knee arthroplasties in patients younger than 40 to the current series. As the authors have noted, patients younger than 60 years of age are likely to be more active than patients older than 60 years; therefore, does it not follow that patients younger than 40 are likely to be substantially more active than patients younger than 60?

In two recent reports by Lonner et al(4) in patients under 40, and Mont et al(5)in patients under the age 50, who had undergone total knee arthroplasty, the results were comparable to those reported in this study of unicompartmental knee arthroplasties.

In the younger active patient, we would also consider the use of joint preserving alternatives such as osteotomies of the proximal tibia and distal femur in the treatment of unicompartmental arthritis. These procedures may last 10 years or longer and can be converted to total knee arthroplasty.(6,7) It does not appear that in this study, biologic alternatives were utilized in any patient prior to unicompartmental arthroplasty. Could the authors comment on other alternatives and whether they were offered or considered?

References 1) Font-Rodriguez DE, Scuderi GR, Insall JN. Survivorship of Cemented Total Knee Arthroplasty. Clin Orthop. 1997; 345:79-86. 2) Buechel FF Sr, Buechel FF Jr, Pappas MJ, Dalessio J. Twenty-year Evaluation of the New Jersey LCS Rotating Platform Knee Replacement. J Knee Surg. 2002; 15:84-89. 3) Keating EM, Meding JB, Faris PM, Ritter MA. Long-Term Followup of Nonmodular Total Knee Replacements. Clin Orthop. 2002; 404:34-39. 4) Lonner JH, Hershman S, Mont M, Lotke PA. Total Knee Arthroplasty in Patients 40 Years of Age and Younger with Osteoarthritis. Clin Orthop. 2000; 380:85-90. 5) Mont MA, Lee CW, Sheldon M, Lennon WC, Hungerford DS. Total Kee Arthroplasty in Patients <50 Years Old. J Arthroplasty. 2002; 17:538 -543. 6) Choi HR, Hasegawa Y, Kondo S, Shimizu T, Ida K, Iwata H. High Tibial Osteotomy for Varus Gonarthrosis: A 10- to 24-year Follow-up Study J Orthop Sci. 2001;6:493-497. 7) Marti RK, Veragen RA, Kerkhoffs GM, Moojen TM. Proximal Tibial Varus Osteotomy. Indications, technique, and five to twenty-one-year Results. J Bone Joint Surg Am. 2001;83:164-70.

Sincerely,

Hari P. Bezwada, MD