All radiographic measurements were obtained in a blinded fashion to avoid bias. To avoid magnification error, the radiographs were taken with standardized markers. To determine the validity of a magnification factor, the following measurements were compared with their adjusted value (value times magnification factor): change in joint line, change in patella tendon distance, change in patella height above the joint line, medial resection, and lateral resection. In all instances there was a significant difference (p = 0.001). Thus, the remainder of the statistical analysis and data presented are with the corrected values in each radiograph to compensate for magnification. The depth of the proximal tibia was measured in the AP radiograph at the level of the proximal tibiofibular joint before and after surgery. The magnification factor averaged 4% (range, 3%-6%). Patients were evaluated clinically with the Knee Society knee score at their latest followup. Knee Society knee scores were generated at each postoperative visit by the same clinical nurse, who had no knowledge of the current study.
The average age of patients was 70 years (Tables 1-3). Osteoarthritis was present in 78% in the group followed up more than 8 years. Eighty-five percent of the patients were female, and the 10-year survival analysis was 95%.
In Groups 1 and 2, the anatomic valgus axis was less than 4° in 66% and 59% of patients, and in the anatomic range of 5° to 8° in only 24% and 26% of patients, respectively. The remainder of the demographics and evaluations are as stated in Tables 1, 2, 3.
Tibial radiolucencies were present in 41 of the 195 knees in Group 1 patients and 30 of the 106 knees in the Group 2 patients. Medial radiolucencies were more common in the knees of patients in both groups. They were present in 12 of 41 (30%) knees in Group 1 patients and in eight of 30 (27%) knees in Group 2 patients. Complete radiolucency was present in eight of 41 patients in Group 1 and nine of 30 patients in Group 2.
The average medial resection was 2.5 mm in Group 1 and 3.03 mm in Group 2. The maximum for both was 14 mm. The average lateral resection was 5.48 mm in Group 1 and 5.71 mm in Group 2, with a maximum of 22 mm for both. In Group 1, the average postoperative joint line elevation was 2.89 mm, and the range was 22 mm of depression to 18 mm of elevation; for Group 2, the average postoperative joint line elevation was 2.60 mm, and the range was 22 mm of depression to 17 mm of elevation. The average patellar tendon length contracted 0.20 mm, with a contraction of 36 mm to a lengthening of 21 mm in Group 1, compared with an average of 1.04 mm in Group 2, with a range of 36 mm of contraction to 21 mm of lengthening. After surgery, in Group 1, 59% and in Group 2, 57% of the patellas remained within 5 mm of the original joint line.
Medial and lateral resection levels were broken down separately into 0 to 5 mm and greater than or equal to 6 mm and were compared with radiolucencies, range of motion, and Knee Society knee score. No significant correlation was seen (Table 4). To delineate these results, both resection levels were divided into 0 to 3 mm and 4 to 5 mm (Table 4). Again, no significant correlation was determined. Thus, there was no effect imposed on the results of a total knee replacement, despite the level of resection.
There were 18 knees with resection levels greater than 10 mm, six (31%) of which had radiolucency, which is not statistically different from the 30 of 106 knees in Group 2 (28%).
Change in the patella height above the joint line was divided into less than 5 mm and greater than 5 mm. A significant value was obtained with a value greater than 5 mm and radiolucencies (Table 5). Patella tendon lengthening or contraction of less than 5 mm, as compared with greater than 5 mm, showed no significant association (Table 5).
The change in the level of joint line from the original joint line was divided into two groups: less than 8 mm and greater than 8 mm. Significance was shown only with an elevation of less than 8 mm and a higher Knee Society score but was not significant in Group 2 (Table 5). Thus, there was no true clinical effect imposed on the results of a total knee replacement, despite the level of resection.
Careful analysis of these failures offered no explanation because no similarities were observed. Two patients had rheumatoid arthritis, but the rest were within the accepted standard profile of patients with osteoarthritis who have total joint replacement. None of the patients who had a failed arthroplasty had resection levels greater than 10 mm (tibial resection levels were 3, 3, 3, 4, 4, 4, 6, 6 mm). Techniques involving bone preparation, cementing, and resection levels and change in joint line offered no clues to the failure of the arthroplasties.
Failure of total knee arthroplasties most commonly is attributed to aseptic loosening of the tibial component.4,5,10,15 Dorr et al,5 Insall,12 Bartel et al,1 and other authors agree that the strongest bone in the tibia resides in the most proximal portion.2-4,9,12,16 The contribution made by the cortex has been challenged.11 The strength decreases from the subchondral bone distally, but the controversy exists regarding the degree of loss, especially after 3 mm.3,9
One study by Dorr et al5 determined that the amount of tibial resection was the most important factor in the appearance of radiolucent lines. Recommendations were made to minimize the amount of tibial resection. However, radiolucencies are a poor predictor of future failure unless they are complete and progressive.15 The data reported by Goldstein et al8 show that strength does decrease with increasing resection, but these changes are minor through the first 2 cm. Harada et al9 showed a dramatic decrease in strength within the first 2.5 mm but with little change with additional resection. Volz et al.16 showed that the compressive strength of cancellous bone in the proximal tibia at 20 mm was 105% of that at 10 mm in the lateral plateau. The medial plateau showed similar results of 96% of compressive strength at the same levels. At 3 cm, the strength was dramatically less. These studies add support to the finding of the current study that proximal tibial resection levels of less than 2½ cm are not clinically significant.
Minimizing bony resection to provide fixation in the strongest part of the proximal tibia is not without concerns. Much has been written to provide evidence that thin polyethylene implants can lead to failure.6,18 In their analysis of failure of polyethylene inserts, Collier et al3 recommended more moderate proximal tibial resection levels to allow the surgeon to implant a thicker component. In addition, in posterior cruciate ligament retaining prostheses, proximal joint line elevation can lead to altered biomechanics and an increased likelihood of failure and unsatisfactory results.7 Moderate tibial resection would minimize these concerns.3,11
If the strength of the proximal tibia is of such importance to the stability of the tibial component, failures should be seen early after implantation because the bone would be unable to remodel and would fail. In today's environment of recommended metal backed tibial components, much less strength is required of the proximal tibia.2,17 Thus, currently used cemented tibial components, if implanted correctly, should not fail secondary to the tibial resection level.
Beneficial effects of bone surface preparation and cementing techniques in relation to the presence of radiolucencies were reported recently.14 Because the current study evaluates arthroplasties during a broad range of time, it is necessary to delineate the factor of differing cement techniques and bone surface preparation in production of radiolucencies. This would confirm that the independent variable of proximal tibial resection level, rather than cementing technique, would be the cause of radiolucencies. Among the original 422 patients, eight prosthetic failures were found.
This current long term retrospective review was performed to determine the effect that proximal tibial resection has on the functional result and survival of posterior cruciate condylar total knee arthroplasties. This long term clinical and radiographic study shows that the level of proximal tibia resection is not clinically significant, and that by resecting moderate amounts of proximal tibia, thicker tibial inserts can be used and the joint line maintained. However, the average resection level on the medial side was 3 mm and on the lateral side 5 mm in the current study.
1. Bartel DL, Bicknell VL, Wright I, Wright TM: The effect of conformity, thickness, and material on stresses in ultra-high molecular weight components for total joint replacement. J Bone Joint Surg 68A:1041-1051, 1986.
2. Bartel DL, Burstein AH, Santavicca EA, Insall JN: Performance of the tibial component in total knee replacement. J Bone Joint Surg 64A:1026-1033, 1982.
3. Collier JP, Mayor MB, McNamara JL, Surprenant VA, Jensen RE: Analysis of the failure of 122 polyethylene inserts from uncemented tibial knee components. Clin Orthop 273:232-242, 1991.
4. Dorr LD, Boiardo RA: Technical considerations in total knee arthroplasty. Clin Orthop 205:5-11, 1986.
5. Dorr LD, Conaty JP, Schreiber R, Mehne DK, Hall D: Technical Factors that Influence Mechanical Loosening of Total Knee Arthroplasty. In Dorr LD (ed). The Knee Papers of the First Scientific Meeting of The Knee Society. Baltimore, University Park Press 121-135, 1985.
6. Engh GA, Dwyer KA, Hanes CK: Polyethylene wear of metal backed tibial components in total and unicompartmental knee prostheses. J Bone Joint Surg 74B:9-17, 1992.
7. Figgie HE, Goldberg VM, Heiple K, Moller HS, Gordon NH: The influence of tibial patellofemoral location on function of the knee in patients with the posterior stabilized condylar knee prosthesis. J Bone Joint Surg 68A:1035-1040, 1986.
8. Goldstein SA, Wilson DL, Sonstegard DA, Matthews LS: The mechanical properties of human tibial trabecular bone as a function of metaphyseal location. J Biomech 16:965-969, 1983.
9. Harada Y, Wevers HW, Ing P, Cooke TDV: Distribution of bone strength in the proximal tibia. J Arthroplasty 3:167-175, 1988.
10. Hofmann AA, Bachus KN, Yatt RWB: Effect of the tibial cut on subsidence following total knee arthroplasty. Clin Orthop 269:63-69, 1991.
11. Hvid I, Jensen J, Nielsen S: Contribution of the cortex to epiphyseal strength. Acta Orthop Scand 56:256-259, 1985.
12. Insall JN: Presidential address to the Knee Society: Choices and compromises in total knee arthroplasty. Clin Orthop 226:43-48, 1988.
13. Lotke PA, Ecker ML: Influence of positioning of prosthesis in total knee replacement. J Bone Joint Surg 59A:77-79, 1977.
14. Ritter MA, Herbst SA, Keating EM, Faris PM: Radiolucency at the bone cement interface in total knee replacement. J Bone Joint Surg 76A:60-65, 1994.
15. Vince KG, Insall JN, Kelly MA: The total condylar prosthesis. J Bone Joint Surg 71B:793-797, 1989.
16. Volz R, Kantor SM, Howe C, McMurtey M: Factors Affecting Tibial Component Stability: A Comparative Study. In Rand JA, Dorr LD (eds). Total Arthroplasty of the Knee: Proceedings of the Knee Society. Rockville, MD, Aspen Publishing 109-120, 1987.
17. Walker PS, Greene D, Reilly D, et al: Fixation of tibial components of knee prosthesis. J Bone Joint Surg 63A:258-267, 1991.
© 1999 Lippincott Williams & Wilkins, Inc.
18. Wright TM, Bartel DL: The problem of surface damage in polyethylene total knee components. Clin Orthop 205:67-74, 1986.