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Functional Results of Navigated Minimally Invasive and Conventional Total Knee Arthroplasty: A Comparison in Bilateral Cases

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Abstract

This prospective study aimed to compare the clinical and radiologic results achieved using navigation-assisted minimally invasive surgery (NA-MIS) and conventional techniques in 42 patients who underwent bilateral total knee arthroplasty (TKA), with a minimum 1-year follow-up. Patients who underwent NA-MIS TKA showed better Hospital for Special Surgery (HSS) Scores and Western Ontario MacMaster (WOMAC) total scores for up to 6 months postoperatively than patients who underwent conventional TKA, and lower WOMAC pain score for up to 9 months postoperatively. Range of motion (ROM) was comparable in both groups at all times. More patients preferred the NA-MIS procedure to the conventional procedure. Radiologic results for the NA-MIS group showed fewer outliers than did results for the conventional group, but not in mean values.

Researchers report good results for minimally invasive total knee arthroplasty (TKA) with regard to early postoperative recovery and reduced soft tissue trauma.^1-5 Minimally invasive surgery (MIS) TKA has potential issues of component malpositioning arising from a limited surgical view, however, and some series have raised questions about component positioning.^6,7

Computer-assisted navigation systems were introduced to improve component alignment accuracies, and a number of studies conclude that leg and component alignment are improved in TKA performed using navigation systems.^8-11 This study combines the accuracy of navigation systems with MIS to solve the challenges caused by a limited surgical view in MIS TKA.¹¹ In a preliminary study,¹² the MIS technique using a navigation system was associated with a rapid functional recovery without compromising component and leg alignments. Moreover, results based on comparisons in the same types of patients eliminate the variability introduced by differences in gender, age, body mass index, comorbidities, and activity levels. In addition, the bilateral comparative approach might expose subtle differences between the two modalities.

Using a bilateral approach, the short-term clinical and alignment accuraries of legs and components achieved using navigation-assisted (NA) MIS with accuracies achieved using conventional TKA were compared and the durability of the early postoperative improvements reported for NA-MIS TKA were examined.

Materials and Methods

Patients (N=45) scheduled for simultaneous NA-MIS TKA and contralateral conventional TKA were enrolled in this prospective study after approval by an institutional review board and written informed consent from all participating patients. In all patients one knee was assigned to NA-MIS and the other to conventional TKA on an alternating basis. One patient whose knee was scheduled for NA-MIS TKA was switched to conventional TKA because of registration failure, and 2 patients were lost to follow-up, leaving 42 patients with a minimum 1-year follow-up available for study.

One surgeon performed over 100 conventional TKA, 30 MIS and 20 NA-MIS TKA before this trial.

MIS was defined as surgery performed via a curvilinear skin incision medial to the patella, from 2 cm proximal to the superior pole of the patella to 2 cm below the joint line, using a midvastus approach without patella eversion. Skin incision length varied between 9 cm and 13 cm. The OrthoPilot (B. Braun Aesculap, Tuttlingen, Germany) navigation system used in the study is an image-free system that uses kinematic analysis of hip, ankle, and knee joints and anatomic mapping of the knee joint to build a working model of patient’s knee, as described previously.^8,9 The authors used a free-hand technique under navigation control when fixing the cutting tibial and femoral jig to bone.

On contralateral sides, conventional TKA was performed using a medial parapatellar arthrotomy, extending about 3 cm to 4 cm into the quadriceps tendon, with patella eversion. Intramedullary instrumentation was used for femoral alignment, and a 6° valgus cut was selected for all knees. The tibial cut was performed with extramedullary instrumentation and made perpendicular to the tibial shaft in both the coronal and sagittal planes. Alignment was checked with extramedullary rods referenced to the anterior superior iliac spine (ASIS) and 5 mm to 10 mm medially from the midpoint of both malleoli. In both surgical groups, the posterior cruciate ligament was retained, and the patella was not resurfaced. In addition, e.motion (B. Braun Aesculap) prostheses were used for arthroplasty, and all were cemented.

Patients in both groups underwent the same postoperative rehabilitation protocol, with active range of motion (ROM) exercise begun within the first few hours. Weight-bearing with an assisting device (a walker or crutch) and active and passive ROM exercises were started on the first postoperative day and were progressed according to patient tolerance.

Average patient age was 64.2 years (range: 48-82 years), and patient population included 9 men and 33 women. Primary diagnoses included osteoarthritis in all patients, and no patient had undergone a previous knee operation.

Clinical evaluations were performed preoperatively and at 3, 6, and 9 months’, and 1 year postoperatively. Clinical results included ROM, Hospital for Special Surgery (HSS) scores, Western Ontario MacMaster (WOMAC) (pain, function) scores, and complications. In addition, the subjective preferences of patients were evaluated at 1 year postoperatively. No significant differences in preoperative ROM, HSS score and deformity were observed between the two groups. Radiologic indices, including mechanical axis (optimum, 0°) and coronal inclinations of the femoral (optimum, 90°) and tibial prostheses (optimum, 90°) on standing anteroposterior (AP) radiographs of knees taken at 1 year after surgery, were measured by a resident independent of the surgical unit. Outcome was defined as acceptable when within ±3° of optimum and as an outlier when >3° of optimum.

Independent and paired Student’s t tests and ² tests were used to compare the two groups. All analyses were performed using SPSS software (SPSS for Windows Release 11.0, Chicago, Ill), and significance was set at 95%.

Results

Preoperative average HSS scores were 68.5 (range: 51-83) in the NA-MIS group and 66.5 (range: 46-81) in the conventional group, and the scores improved to 93.6 (range: 85-100) and 92.5 (range: 77-100) at 1 year postoperatively, respectively (P< .01 for both groups). Patients in the NA-MIS group had a higher average HSS score than did patients in the conventional group at 6 months’ postoperatively (P=.042) but not after 9 months’ postoperatively (P=.111). The clinical results are shown in Tables 1 and 2.

In terms of WOMAC scores, pain scores in the NA-MIS group were lower than those in the conventional group for up to 9 months’ postoperatively (P=.020), but not at 1 year postoperatively (P=.122). Total scores showed better results up to 6 months’ (P=.031), but not after 9 months’ postoperatively (P=.297) (Tables 1 and 2).

Preoperatively, ROM average 115.5° in the NA-MIS group and 117° in the conventional group, and ROM improved to 131.6° and 127.1° at 1-year follow-up, respectively (P<.05 for both groups). These results however, were not significantly different at any stage during follow-up between the two groups (P>.05) (Tables 1 and 2). Of the patients, 24 preferred the NA-MIS procedure, 10 for the CON procedure, and 8 patients showed no preference (P=.003). Deep infection or loosening requiring revision did not occur in either group during follow up.

Mean mechanical axes were not significantly different in the two groups (varus 0.7±1.6° and varus 0.8±2.5°, respectively) (P=.815). The conventional group (n=8), however, had more outliers than did the NA-MIS group (n=2) (P=.043). In the coronal alignment of the femoral component, the conventional group (n=9) had more outliers than did the NA-MIS (n=3) group. Significant differences (P=.061) were not observed in outlier and mean values (88.9±2.6° in the NA-MIS group and 88.7±2.8° in the conventional group; P=.769). No differences were observed between the two groups in terms of means (P=.365) or outliers (P=.645) for coronal tibial alignment.

Discussion

Minimally invasive TKA may be an ideal option for reducing blood loss, postoperative pain, and hospitalization and for promoting recovery. Investigators report that TKA using an MIS technique leads to rapid recovery from surgery, short hospital stays, and an improved ROM during the early postoperative period.^1-5 In minimally invasive TKA, component malpositioning and neurovascular injury may arise due to a limited surgical exposure, however.^6,7 Moreover, computer navigation has been demonstrated to reduce the number of component coronal plane outliers in TKAs,^8-11 and thus, the authors considered that the coupling of computer navigation and MIS-TKA is likely to be beneficial.

In a preliminary report on minimally invasive TKA, the authors reported that NA-MIS TKA resulted in lower pain scores, shorter times to achieve 90° flexion and straight-leg raise, and a smaller extension lag during the early postoperative period (within 2 weeks).¹² No previous study has presented the functional results of NA-MIS TKA.

Therefore, the authors performed this study to determine the comparative longevity of early postoperative results, it’s the first to compare the functional results of MIS techniques using a navigation system and a conventional technique in bilateral knee joints after TKA. The duration of the benefit of MIS in TKA postoperatively is debatable. Laskin et al showed that the benefit disappears before 3 months’ postoperatively, whereas Haas et al found that the benefit was evident at 1 year postoperatively.^4-6 In this study, the authors found that the NA-MIS group showed better results than the conventional group in HSS and WOMAC (pain and total) scores until 6 months postoperatively but no benefit in ROM at 3 or 6 months postoperatively.^4,5 At 1 year postoperatively, no measurable differences were found between NA-MIS and CON techniques, and more patients were satisfied with the NA-MIS technique.

The data confirm the results of previous investigations that found a reduction in the number of coronal plane alignment outliers for computer navigation versus traditional manual instrumentation without navigation.

In conclusion, NA-MIS TKA using a mini-midvastus approach results in better knee functional scores after TKA than does conventional TKA, up to 6 or 9 months’ postoperatively. No differences in any functional parameters were evident at 1 year postoperatively. NA-MIS TKA had fewer prosthetic alignment outliers than did conventional TKA. A larger cohort and longer-term studies are needed to determine whether this reduction in outliers results in improved prosthetic survival.

References

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Authors

Drs Song, Seon, Yoon, Park, Bae, and Cho are from the Center for Joint Diseases, Chonnam National University Hwasun Hospital, Jeonnam, Korea.