The Usefulness of a Simplified Navigation-Based Instrumentation for a Novice Surgeon in Primary Total Knee Arthroplasty: A Retrospective Analysis of a Randomized Controlled Trial

Patient Selection

Between January 2020 and July 2020, a total of 144 knees (78 patients) that underwent consecutive primary TKA were retrospectively reviewed. Inclusion criteria for this study were as follows: patients (1) with symptomatic progressed osteoarthritis (Kellgren-Lawrence grade ≥ III), (2) over 60 years of age, (3) with a minimum follow-up period of 24 months, and (4) with use of the navigation-based instrumentation system (ExactechGPS, TKA Plus) or a conventional technique. Four knees that underwent primary TKAs using a full-navigation option (3 with IM nails; 1 with extra-articular femoral deformity secondary to malunited femoral shaft fractures) were excluded.14, 15) A computer randomization system was used to allocate the patients to either the navigation-based instrumentation system cohort (group A, n = 70) or the conventional cohort (group B, n = 70). During the study period, 5 knees were lost to follow-up (3 in group A, 2 in group B). Finally, 135 knees were enrolled in the current study and assigned to either group A (n = 67) or group B (n = 68) (Fig. 1).

Fig. 1
Flow diagram for enrolled patients (numbers of knees). TKA: total knee arthroplasty.

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All operations were performed by a novice surgeon (GBK) in a single institute using the same posterior-stabilized prosthesis (Truliant Knee System, Exactech). All prostheses were used with cement. The novice surgeon completed a 2-year fellowship for TKA, independently performed TKA within 1 year, and had no previous experience with navigation-assisted TKA alone.16, 17)

Surgical Technique Using a Simplified Navigation-Based Instrumentation System

ExactechGPS TKA Plus is a novel hybrid system of cutting-aided device with minimal deviation from conventional surgical techniques based on the global positioning system (GPS) of navigation. This instrument facilitates cutting of the distal femur and proximal tibia and is different from the computer navigation system equipped with a full-option system that provides information on femoral component rotation and extension and flexion gaps.

A medial parapatellar arthrotomy with a midline incision was performed. All osteophytes were removed from the femur and tibia. The femur was first prepared in all cases. After entering the basic information, the femoral and tibial trackers were connected and calibrated. A distal femoral resection guide with adjusting knobs was combined with the distal femoral alignment guide of an existing implant. Then, while inserting the IM rod, the assembled device was seated on the distal femur and fixed with two threaded pins (Fig. 2A). After removal of the IM rod and distal femoral alignment guide, a femoral tracker was placed on the section guide to prepare the acquisition of the femoral implant. For implant acquisition, the hip center, knee center, posterior femoral condyles, and distal femoral condyles were enrolled as tracker probes. While checking the degree of distal femoral cut on the screen, the surgeon controlled the adjusting knobs to modify the varus/valgus and flexion/extension of the distal femoral resection guide in units of 1°, enabling fine-tuning to desired cut parameters. In all cases, the degree of varus/valgus of the distal femur was set at 0°, and then bone resection was performed. Once the desired cut parameters were set, the resection guide was finally secured with a threaded pin to prevent movement. After distal femoral resection, the cutting accuracy was verified by placing a femoral resection tracker on the cutting surface (Fig. 2B).

Fig. 2
Resection process of the distal femur using TKA Plus. (A) A distal femoral resection guide equiped with adjusting knobs was combined with the distal femoral alignment guide of the implant. After the intramedullary rod insertion, the assembled device was seated on the distal femur and fixed with two threaded pins. (B) The cutting accuracy was verified by placing a femoral resection tracker on the cutting surface.

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The proximal tibial cut was performed using an extramedullary (EM) guide with adjusting knobs. After setting the rough cutting level with the tibial stylus, the tibial resection guide was secured with the first two threaded pins. Then, the tibial tracker was mounted on the resection guide (Fig. 3A). For implant acquisition, both malleoli, the center of the tibial spine, the direction of the sagittal plane, and both plateaus were enrolled as tracker probes. While checking the degree of proximal tibial cut on the screen, the surgeon controlled the adjusting knobs to modify varus/valgus and flexion/extension of the proximal tibial resection guide in units of 1°, which enabled fine-tuning to the desired cut parameters (Fig. 3B). As with the distal femur, after the degree of varus/valgus of the proximal tibia was set at 0°, bone resection was performed. Once the target cut parameters were decided, the resection guide was finally secured with a threaded pin to prevent movement. After proximal tibial resection, the cutting accuracy was checked by placing a tibial resection tracker on the cutting surface (Fig. 3C). Finally, the extension gap was checked by inserting a spacer block, and then all instruments were removed.

Fig. 3
Resection process of the proximal tibia using TKA Plus. (A) After setting the rough cutting level with the tibial stylus, the tibial resection guide was secured with the first two threaded pins. Then, the tibial tracker was mounted on the resection guide. (B) The surgeon could control the adjusting knobs to modify the degree of proximal tibial cutting in 1° increments, enabling fine tuning to the desired cut parameters. (C) The cutting accuracy was checked by placing a tibial resection tracker on the cutting surface.

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The remaining surgical procedures were performed using the modified gap-balancing technique, with which the extension gap could be balanced before the flexion gap18) using the same posterior-stabilized femoral implant. Femoral component rotation was determined according to the balanced flexion gap.19) Femur sizing was performed using an anterior reference system. The rotation of the tibial component was set by considering several reference points, including the medial one-third of the tibial tuberosity, anterior tibial cortex, and floating technique.20) All prostheses were fixed with cement. Antioxidant polyethylene inserts were used in all cases. Patellar resurfacing was selectively performed in patients with intraoperatively identified International Cartilage Repair Society grade III or IV lesions.21)

Conventional TKA Technique

The conventional technique was also implemented based on the modified-gap balance technique.18) A medial parapatellar arthrotomy with a midline incision was performed. After removing all osteophytes from the femur and tibia, an IM alignment rod for distal femur cut was set with the goal of achieving 5°–6° valgus depending on alignment. A standard EM jig for the proximal tibia was used with the aim of cutting the bone perpendicular to the tibial axis. Femoral component rotation was determined according to the balanced flexion gap. Femur sizing was performed using an anterior reference system in all cases. All other procedures were performed in the same way as the surgical procedure using a navigation-based instrumentation system.

Postoperative Management

A single closed suction drain was maintained for 24 hours after surgery. All patients received an identical perioperative pain control protocol, including a multimodal drug regimen, postoperative patient-controlled analgesia, and intraoperative periarticular injection. The active dangling exercise was initiated on the day of surgery, and partial weight-bearing with a crutch was allowed on the first postoperative day. Full weight-bearing was permitted 3 weeks after surgery.

Outcome Assessments

The demographic characteristics were recorded before surgery. The operative details including tourniquet time and drainage amount were also investigated through medical records. Radiographic and clinical outcomes of each patient were assessed preoperatively, at 6, 12, and 24 months postoperatively, and annually thereafter. At each follow-up, the outcomes of group A and group B were compared.

Bilateral standing anteroposterior and lateral radiographs and scanograms were used to assess lower limb alignment and component position. The hip-knee-ankle (HKA) angle was defined as the angle between the femoral and tibial mechanical axes on scanograms (varus alignment indicated as a negative value).22) The outliers were considered to be more than ± 3° of 0° (neutral mechanical alignment).3) The position of components in the coronal and sagittal planes was evaluated using α, β, γ, and δ angles by the Knee Society radiological evaluation method.23) The outliers of component positions were defined as those lying outside ± 3° of 6° (α angle), 90° (β angle), 0°–10° (γ angle), and 3° (δ angle).3)

Radiologic measurements were performed twice at least 2 weeks apart by two independent observers (OJS and HGL) who had no clinical contact with the patients to evaluate intra- and interobserver reliability. Reliability for all radiographic parameters was analyzed using intraclass correlation coefficients and classified as little if any (correlation coefficient, ≤ 0.25), low (0.26–0.49), moderate (0.50–0.69), high (0.70–0.89), or very high (≥ 0.90).24) All measurements were performed using a picture achieving and communication system (PiViewSTAR, Infinitt Co.).

For clinical assessments, Knee Injury and Osteoarthritis Outcome Score for Joint Replacement25) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) for pain and function26) were investigated. They were recorded by an independent researcher (HGL) in the outpatient clinic. Range of motion (ROM) of the knee joint including flexion contracture and further flexion angle was measured using a standardized manual goniometer with a 30-cm plastic movable long arm. The values at the final follow-up were compared with the preoperative values. The incidence of complications including infection and aseptic loosening was also investigated via chart review.

Statistical Analysis

Statistical evaluation was performed using IBM SPSS software ver. 25 (IBM Corp.) and continuous data were expressed as mean ± standard deviation or mean with range. All dependent variables were tested for normality of distribution and equality of variances using the Kolmogorov-Smirnov test and were analyzed using non-parametric tests because they showed non-normal distributions. Radiographic and clinical outcomes were compared between groups A and B using an independent samples t-test. The preoperative and postoperative radiographic and clinical outcomes were also compared using paired t-tests. The proportion of patients in each group was compared using the chi-square test. For all tests, a p-value < 0.05 was considered statistically significant. Moreover, a post-hoc power analysis was performed to evaluate whether the sample had sufficient power to detect significant differences using the significance set at an α of 0.05. A statistical power > 90% based on the enrolled sample size was considered to be sufficient, and all of the variables that were significantly different met this criterion.27) Therefore, it was determined that our study was adequately powered.