Abstract
Background
Restoration of posterior condylar offset (PCO) during TKA is believed to be an important to improve knee kinematics, maximizing range of motion (ROM) and minimizing flexion instability. The aim of prospective study was to find out the role of PCO in post-operative ROM after cruciate retaining (CR) and cruciate sacrificing (CS) TKA.
Methods and materials
A total of 90 patients were divided into the CR knee group (49) and CS knee Group (41) intra-operatively by the surgeon based on the status of Posterior Cruciate Ligament. Preoperative and postoperative PCO was evaluated on true lateral knee radiographs. The ROM was measured pre operatively and post operatively at 4 weeks, 8 weeks, 3 months, 1 year and 2 years. Appropriate statistical tests were used and results were interpreted.
Results
The mean flexion angle was 113.86° in CR knees and 118.29° in CS knees with a significantly greater improvement observed for the latter group. Preoperative mean PCO was 35.08 mm in CR knees and 36.37 mm in CS knees, while the corresponding values post operatively were 32.74 mm and 34.88 mm respectively, at follow-up. In order to evaluate the relationship between change of PCO and postoperative improvement in range of flexion, we divided the patients into three sub groups according to the difference in pre and post-operative PCO. The first sub group had a difference in PCO ≤ 1 mm after surgery (CR: 5 and CS: 8), second sub group with a difference in PCO 1–3 mm after surgery (CR: 28 and CS: 26) and the third subgroup with a difference in PCO >3 mm after surgery (CR: 16 and CS: 7). Then a comparison of difference in PCO and post-operative range of motion was done in both CR knees and CS knees separately. The final post-operative range of motion (flexion) in CR knees was 117.6°, 115.93° and 109.06° for the three subgroups respectively. Similarly, the final post-operative range of motion (flexion) in CS knees was 116.12°, 118.81° and 118.86° for the three subgroups respectively. Thus a significant difference between three sub groups was observed in CR knees (P < 0.0001), while no difference was observed in the PS knees.
Conclusion
The postoperative decrease in posterior condylar offset by more than 3 mm decreases the post-operative ROM in CR TKA but not in CS TKA. So it is critical to preserve PCO in CR but perhaps not CS knees to ensure optimal ROM postoperatively.
Keywords: Posterior condylar offset, ROM, Cruciate retaining, Cruciate sacrificing, Total knee arthroplasty, TKR
1. Introduction
Painless functional range of motion is the goal of Total Knee Arthroplasty (TKA). Post-operative flexion range is important for daily activities like ascending stairs and sitting. The minimum knee flexion necessary for daily living is widely agreed to be about 90°.1, 2, 3, 4 Asian population requires more flexion range because of life style needs such as cross-legged sitting, squatting that requires deep knee flexion up to 150–160°. However, after TKA flexion beyond 120° is infrequent and this adversely affects patient reported outcome scores. The determinants of range of motion (ROM) following TKA may be surgically modifiable (Posterior condylar offset, Posterior tibial slope, intra operative ligament balancing, implant design, cruciate retaining or sacrificing procedure) or non-modifiable (diagnosis, preoperative knee flexion, preoperative varus and valgus deformity, Age, Sex, body mass index, postoperative physical therapy).6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 Posterior Condylar Offset (PCO) is defined as the maximum thickness of the posterior condyle to the tangent of posterior cortex of femoral shaft on true lateral radiographs of knee. Restoration of PCO during TKR is believed to be an important parameter to improve knee joint kinematics, maximizing ROM and minimizing flexion instability.17Many clinical and cadaveric experimental studies have sought to determine the restoration of PCO in TKR.14,17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 Some authors have demonstrated improved ROM in Cruciate Retaining (CR) TKR with preserved postoperative PCO; while other have shown no correlation of PCO with knee flexion.14,17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 To date there is only one study that compares the effect of PCO in CR and Cruciate sacrificing (CS) design.Arabori et al. found no statistical correlation between the change in knee flexion and the difference in the PCO after CS TKA.19 There is a paucity of literature to demonstrate the effect of PCO on range of motion in CR or CS TKA.
The aim of this study was comparative analysis of effect of PCO on post-operative range of motion in CR and CS primary TKA for osteoarthritis of knee. Hypothesis was that the change in the PCO (increase or decrease) has inverse relation with post-operative ROM in CR and CS TKA.
2. Methods
This prospective observational study was conducted at a tertiary care center after approval of Institutional Review Board. Ninety consecutive TKR for Kellgren Lawrence grade IV osteoarthritis, operated between November 2015 and May 2017 by the same surgical team, were included. Patients with severe deformity of the knee requiring constrained implant, rheumatoid arthritis and other connective tissue disorders, revision total knee replacement, extra-articular deformity, infection, sepsis, poor extension mechanism, peripheral vascular disease, inadequate soft tissue coverage of knee joint and with morbid obesity were excluded from the study. A complete physical examination was performed in all cases. Preoperative range of motion of the knee was assessed using standard clinical goniometer. A radiographic assessment was done by taking radiographs of bilateral knees antero-posterior view in standing position and a true lateral view in 100% magnification. Preoperative posterior condylar offset (PCO) was determined on true lateral radiographs of knee by measuring the maximal thickness of the posterior condyle, projected posteriorly to the tangent of the posterior cortex of the femoral shaft at 90° of flexion by PACS software (Fig. 1). Pre- operative functional assessment using American knee society score system (AKSS) was done in all patients. All patients underwent total knee replacement by standard midline para patellar approach. All cases were performed by measured resection technique with mechanical alignment. The decision of CR or CS Knee technique was based on the intra-operative finding of intact functional PCL and perfect soft tissue balance during trial stage. In the presence of a nonfunctional PCL; CS knee implant was used. In varus knees if PCL was found tight, contracted (because it being a medial to midline structure) and trial balance was not satisfactory after medial releases, CS implant was used. Femoral component was axially aligned according to condylar twist angle. Tibial cut was sagittal aligned parallel to shin (from mid tibia to just proximal to ankle) with standard 3° posterior slope. Tibial base plate was rotationally aligned to Akagi line. A preoperative note of type of implant that is cruciate retaining (CR) or cruciate sacrificing (CS) was made.
Fig. 1.
Pre operative lateral radiograph of knee showing measurement of PCO.
Ambulation was started after 24 h with the support of a walker and sutures were removed after 14 days of surgery. All cases were subjected to same standard rehab protocol. Post-operative ROM at 4 weeks, 8 weeks, 3 months, 1year and at final follow-up (2 years) was recorded. Posterior condylar offset was measured at 4 weeks post op by the method described (Fig. 2).
Fig. 2.
Post operative lateral radiograph of knee showing measurement of PCO.
In order to evaluate the relationship between the change of posterior condylar offset and the postoperative improvement in range of flexion, we have divided the patients into three subgroups according to the difference in pre and post-operative posterior condylar offset prior to the analysis to prevent observer bias.
The first sub group with difference in PCO measurement between pre-operative and post-operative radiograph was less than or equal to 1mm, second sub group with a difference in PCO 1–3 mm and in the third subgroup with a difference in PCO >3 mm. Finally a comparison of difference in PCO and post-operative range of motion was done in both CR knees and CS knees separately. A postoperative functional assessment using American knee society score system (AKSS) was also recorded at 3 months, 1year and 2 years.
The data was entered in Microsoft EXCEL spreadsheet and analysis was done using Statistical Package for Social Sciences (SPSS) version 21.0. Normality of data was tested by Kolmogorov-Smirnov test. If the normality was rejected, then non parametric test was used. Categorical variables were presented in number and percentage (%) and continuous variables were presented as mean ± SD and median. Quantitative variables were compared using Unpaired t-test/Mann-Whitney Test (when the data sets were not normally distributed) between the two groups and paired t-test/Wilcoxon rank sum test across follow up within the group. Qualitative variables were correlated using Chi-Square test/Fisher's exact test. A p value of <0.05 was considered statistically significant.
3. Results
Out of 90 cases there were 21 males (23.3%) and 69 females (76.6%). Demographic data of the patients are as mentioned in Table 1. Out of the total 90 patients, 49 patients underwent TKA of CR Design and 41 underwent TKA of CS Design (Table 1).
Table 1.
Demographic details and outcomes of CR and CS knee.
| Parameters | CR knees | CS knees | P value |
|---|---|---|---|
| Age (In years) | 65.24 | 65.88 | 0.683 |
| Sex | |||
| Female | 37 (75.51%) | 32 (78.05%) | |
| Male | 12 (24.49%) | 9 (21.95%) | 0.777 |
| Operative Side | |||
| Right | 22 (44.9%) | 19(46.34%) | |
| Left | 27 (55.10%) | 22 (53.56%) | 0.891 |
| Preoperative ROM (in degrees) | 106.74 ± 23.07 | 110.51 ± 12.73 | 0.906 |
| Postoperative ROM(in degrees) | 94.63 ± 7.85 | 95.8 5.23 | 0.632 |
| 4 weeks | 102.18 ± 7.02 | 104 ± 5.72 | 0.15 |
| 8 weeks | 106.45 ± 5.28 | 109.22 ± 4.78 | 0.009 |
| 3 months | 109.92 ± 5.01 | 114.49 ± 3.5 | < 0.001 |
| 1 year | 113.86 ± 5.05 | 118.29 ± 3.52 | < 0.0001 |
| 2 years | |||
| Preoperative PCO (in mm) | 35.08 ± 3.88 | 36.37 ± 3.99 | 0.123 |
| Post-operative PCO (in mm) | 32.74 ± 4.02 | 34.88 ± 3.47 | 0.013 |
| Preoperative AKSS | 47.98 ± 8.08 | 43.32 ± 8.82 | 0.007 |
| Post-operative AKSS | 79.29 ± 5.39 | 80.19 ± 4.27 | 0.732 |
| Final follow up (in months) | 29.22 ± 6.11 | 31.39 ± 6.29 | 0.065 |
The mean age of the patients of both groups is comparable (CR group 65.24 ± 7.68 years and CS group 65.88 ± 6.79 years). Twenty-five cases were in age of 50–60 years, 36 in 61–70 years and rest 29 was more than 70 years.
The pre-operative flexion was 106.74oin CR and 110.51oin CS group. The post-operative flexion was 113.86° and 118.29oin CR and CS group respectively. Nearly 7oof improvement in the range of flexion was noted at the time of final follow up in both the groups. The improvement in ROM was statistically significant (p value < 0.001). There were 5 cases of CR and 8 of CS in first sub group that had a difference in PCO of ≤ 1 mm after surgery. In second sub group that had difference in PCO of 1–3 mm after surgery there were 28 CR and 26 CS. In the third subgroup that had difference in PCO of >3 mm after surgery there were 16 CR and 7 CS. A comparison of difference in PCO and post-operative range of motion was done in both CR knees and CS knees separately. The final post-operative range of flexion in CR group was 117.6 ± 5.06°, 115.94 ± 4.4° and 109.06 ± 1.69° for the three subgroups respectively (Fig. 4, Table 3). The difference between three groups in improvement of ROM was statistically significant (p value of <0.0001) and was found to be best in group 1 in CR cases. The final post-operative range of flexion in CS knees was 116.12 ± 3.48°, 118.81 ± 3.33° and 118.86 ± 3.6° for the three subgroups respectively (Fig. 3, Table 2). The difference between three groups in improvement of ROM was statistically insignificant (p value 0.124) in CS cases. Thus a significant difference between three groups (effect of change in posterior condylar offset on postoperative flexion) was observed in the CR knees (P < 0.001), whereas no difference was observed in the CS knees.
Fig. 4.
Comparison of difference in the ROM in different CR Knee subgroups (as per PCO).
Table 3.
Comparison of difference in ROM in different CR Knee subgroups (as per PCO).
| Difference in PCO in CR knee | Group 1 ≤ 1 mm | Group 2(1–3)mm | Group 3(>3)mm |
|---|---|---|---|
| Pre op | 111.4 | 105.64 | 104.06 |
| 4weeks | 98.6 | 96.54 | 90.06 |
| 8weeks | 104.8 | 104.61 | 97.12 |
| 3months | 110.2 | 108.39 | 101.88 |
| 1year | 113.4 | 112.07 | 105.06 |
| 2years | 117.6 | 115.93 | 109.06 |
Fig. 3.
Comparison of difference in the ROM in different CS Knee subgroups (as per PCO).
Table 2.
Comparison of difference in ROM in different CS Knee subgroups (as per PCO).
| Difference in PCO | Group 1 ≤ 1 mm | Group 2(1–3)mm | Group 3(>3)mm |
|---|---|---|---|
| Pre op | 111 | 109.04 | 115.43 |
| 4weeks | 96.62 | 96.04 | 94 |
| 8weeks | 106.62 | 103.58 | 102.57 |
| 3months | 110.88 | 109.04 | 108 |
| 1year | 112.12 | 115.12 | 114.86 |
| 2years | 116.12 | 118.81 | 118.86 |
The mean pre-operative AKSS score was 47.98 ± 8.08 for CR group and 43.32 ± 8.82 for CS group. The mean AKSS at the time of final follow up improved to 79.29 ± 5.39 for CR group and 80.19 ± 4.27 for CS group. Final reading of AKSS was better in CS group in comparison to CR group but was not statistically significant (p value 0.732).
Additionally a comparison of difference in PCO and post-operative AKSS score was done in both CR knees and CS knees separately. The final post-operative AKSS in CR group was 82.2, 79.82 and 77.44 for the three subgroups respectively (Table 5). The difference between three groups in improvement of ROM was statistically insignificant (p value of 0.188) and was found to be best in group 1in CR cases.
Table 5.
Comparison of difference in AKSS in different CR Knee subgroups (as per PCO).
| Difference in PCO | Group 1 ≤ 1 mm | Group 2(1–3)mm | Group 3(>3)mm |
|---|---|---|---|
| AKSS Pre op | 46 | 49.46 | 46 |
| AKSS 4weeks | 65.4 | 62.61 | 57.12 |
| AKSS 8weeks | 77 | 69.86 | 67.75 |
| AKSS 3months | 81 | 76.25 | 74 |
| AKSS 1year | 82.2 | 80.11 | 76.81 |
| AKSS 2years | 82.2 | 79.82 | 77.44 |
The final post-operative AKSS score in CS knees was 81.25, 79.54 and 81 for the three subgroups respectively (Table 4).The difference between three groups in improvement of AKSS was also statistically insignificant (p value 0.468) in CS cases.
Table 4.
Comparison of difference in AKSS in different CS Knee subgroups (as per PCO).
| Difference in PCO | Group 1 ≤ 1 mm | Group 2(1–3)mm | Group 3(>3)mm |
|---|---|---|---|
| AKSS Pre op | 42.62 | 42.67 | 45.67 |
| AKSS 4weeks | 60.75 | 58.17 | 56.78 |
| AKSS 8weeks | 68.12 | 68.67 | 67.89 |
| AKSS 3months | 76.88 | 74.46 | 77.67 |
| AKSS 1year | 80.12 | 78.62 | 80.44 |
| AKSS 2years | 81.25 | 79.54 | 81 |
4. Discussion
The post-operative knee flexion required for swing phase of the gait, climbing/descending stairs and rising from the chair varies from 67° to 93o.1, 2, 3, 4, 5 Restoration of PCO after TKA is supposed to be an important factor to attain maximum range of flexion. Both CR and CS groups in this study were nearly similar in terms of demographic and clinical characteristics. For measurement of PCO we did not add cartilage thickness of posterior femoral condyle either pre-operative or postoperative so that the change in PCO would remain the same.
In this study we noticed improvement in range of flexion in all cases. The increase in mean ROM in CS group was nearly same as in CR group. In CR cases it was best in group 1 that is when post TKA PCO is closer to pre-operative PCO in CR knee the improvement is statistically significantly better than other CR cases where restoration of PCO is not closer to pre-operative value. Bellemanns et al. reported that the reduction in postoperative PCO correlated with significant decrease in final maximum angle of flexion.17 For every 3 mm decrease in PCO, the maximal obtainable flexion was reduced by a mean of 29.7° in comparison to those knees in which the PCO had been restored within 3 mm. Similarly Massinet al showed that a 3-mm decrease of the PCO could reduce knee flexion by 10° before the occurrence of tibio femoral impingement.
On the contrary we did not notice any loss in flexion even in group 3 where difference in PCO was more than 3 mm. In group 3 also the postoperative ROM was significantly better than preoperative flexion but the magnitude of improvement was lesser than other groups. We also noticed a statistically significant difference between groups in the final obtainable flexion if the difference in PCO was more than 3 mm in CR knee group (P value < 0.0001).
In CS group we found no correlation in change of PCO to final ROM obtained as depicted by statistically insignificant difference between groups. The magnitude of improvement in final ROM was best in group 2, even better than group 1 where PCO was closest to pre-operative value. The opinion regarding effect of PCO on post-operative ROM in existing literature remains divided. Arabori et al., Yang G et al. and Hanratty BM et al. found no statistical correlation between the change in knee flexion and the difference in the PCO after CS TKA. But there are studies that have demonstrated improved range of motion in cruciate retaining TKA with preserved post-operative PCO. We noticed that post-operative ROM in CS knees was proportionately better in cases with better preoperative ROM similar to previously reported.24 In this study postoperative PCO was found to be lesser than preoperative PCO in all cases as posterior referencing was used and upon sizing when it is between two sizes smaller size is chosen. Biomechanically, restoration of PCO prevents the tibio femoral impingement during flexion and there by improves the maximum range of flexion after TKA. When PCO is decreased mechanical block is caused by the impingement of the femur sliding forwards on the tibia during flexion during flexion, resulting in limitation of flexion after CR TKA.17 In CR knees the intact PCL accounts for changes i.e. increased glide in the setting of a reduced PCO leaving the intact PCL more lax27 However biomechanical reason for difference in the PCO not affecting the ROM in CS TKA is not yet clear.
The limitation in this study is relatively small sample size of 90 patients. Factors that may confound postoperative range of motion after TKA, such as posterior tibial slope, degree of deformity, age and sex were not included in our statistical analysis.
5. Conclusion
Restoration of PCO in CR TKA provides optimum range of motion; On the contrary a decrease in PCO by more than 3 mm decreases the post-operative ROM in the CR TKA. Conversely, there is no correlation between the pre- and postoperative change in PCO for postoperative ROM in CS TKAs.
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