Patient specific instrumentation (PSI) uses advanced imaging of the knee (CT or MRI) to generate individualised cutting blocks aimed to make the procedure of total knee arthroplasty (TKA) more accurate and efficient. However, in this era of healthcare cost consciousness, the value of new technologies needs to be critically evaluated. There have been several comparative studies looking at PSI versus standard instrumentation. Most compare PSI with conventional instrumentation in terms of alignment in the coronal plane, operative time and surgical efficiency, cost effectiveness and short-term outcomes. Several systematic reviews and meta-analyses have also been published. PSI has not been shown to be superior compared with conventional instrumentation in its ability to restore traditional mechanical alignment in primary TKA. Most studies show comparative efficacy and no decrease in the number of outliers in either group. In terms of operative time and efficiency, PSI tended towards decreasing operative time, saving a mean of five minutes per patient (0 to 20). Furthermore, while some cost savings could be realised with less operative time and reduced instrumentation per patient, these savings were overcome by the cost of the CT/MRI and the cutting blocks. Finally, there was no evidence that PSI positively affected clinical outcomes at two days, two months, or two years. Consequently, current evidence does not support routine use of PSI in routine primary TKA. Cite this article: Bone Joint J 2016;98-B(1 Suppl A):78–80

Aims. Total knee arthroplasty (TKA) using functional alignment aims to implant the components with minimal compromise of the soft-tissue envelope by restoring the plane and obliquity of the non-arthritic joint. The objective of this study was to determine the effect of TKA with functional alignment on mediolateral soft-tissue balance as assessed using intraoperative sensor-guided technology. Methods. This prospective study included 30 consecutive patients undergoing robotic-assisted TKA using the Stryker PS Triathlon implant with functional alignment. Intraoperative soft-tissue balance was assessed using sensor-guided technology after definitive component implantation; soft-tissue balance was defined as intercompartmental pressure difference (ICPD) of < 15 psi. Medial and lateral compartment pressures were recorded at 10°, 45°, and 90° of knee flexion. This study included 18 females (60%) and 12 males (40%) with a mean age of 65.2 years (SD 9.3). Mean preoperative hip-knee-ankle deformity was 6.3° varus (SD 2.7°). Results. TKA with functional alignment achieved balanced medial and lateral compartment pressures at 10° (25.0 psi (SD 6.1) vs 23.1 psi (SD 6.7), respectively; p = 0.140), 45° (21.4 psi (SD 5.9) vs 20.6 psi (SD 5.9), respectively; p = 0.510), and 90° (21.2 psi (SD 7.1) vs 21.6 psi (SD 9.0), respectively; p = 0.800) of knee flexion. Mean ICPD was 6.1 psi (SD 4.5; 0 to 14) at 10°, 5.4 psi (SD 3.9; 0 to 12) at 45°, and 4.9 psi (SD 4.45; 0 to 15) at 90° of knee flexion. Mean postoperative limb alignment was 2.2° varus (SD 1.0°). Conclusion. TKA using the functional alignment achieves balanced mediolateral soft-tissue tension through the arc of knee flexion as assessed using intraoperative pressure-sensor technology. Further clinical trials are required to determine if TKA with functional alignment translates to improvements in patient satisfaction and outcomes compared to conventional alignment techniques. Cite this article: Bone Joint J 2021;103-B(3):507–514

Aims. It is unknown whether kinematic alignment (KA) objectively improves knee balance in total knee arthroplasty (TKA), despite this being the biomechanical rationale for its use. This study aimed to determine whether restoring the constitutional alignment using a restrictive KA protocol resulted in better quantitative knee balance than mechanical alignment (MA). Methods. We conducted a randomized superiority trial comparing patients undergoing TKA assigned to KA within a restrictive safe zone or MA. Optimal knee balance was defined as an intercompartmental pressure difference (ICPD) of 15 psi or less using a pressure sensor. The primary endpoint was the mean intraoperative ICPD at 10° of flexion prior to knee balancing. Secondary outcomes included balance at 45° and 90°, requirements for balancing procedures, and presence of tibiofemoral lift-off. Results. A total of 63 patients (70 knees) were randomized to KA and 62 patients (68 knees) to MA. Mean ICPD at 10° flexion in the KA group was 11.7 psi (SD 13.1) compared with 32.0 psi in the MA group (SD 28.9), with a mean difference in ICPD between KA and MA of 20.3 psi (p < 0.001). Mean ICPD in the KA group was significantly lower than in the MA group at 45° and 90°, respectively (25.2 psi MA vs 14.8 psi KA, p = 0.004; 19.1 psi MA vs 11.7 psi KA, p < 0.002, respectively). Overall, participants in the KA group were more likely to achieve optimal knee balance (80% vs 35%; p < 0.001). Bone recuts to achieve knee balance were more likely to be required in the MA group (49% vs 9%; p < 0.001). More participants in the MA group had tibiofemoral lift-off (43% vs 13%; p < 0.001). Conclusion. This study provides persuasive evidence that restoring the constitutional alignment with KA in TKA results in a statistically significant improvement in quantitative knee balance, and further supports this technique as a viable alternative to MA. Cite this article: Bone Joint J. 2020;102-B(1):117–124

Aims. The purpose of the present study was to compare patient-specific instrumentation (PSI) and conventional surgical instrumentation (CSI) for total knee arthroplasty (TKA) in terms of early implant migration, alignment, surgical resources, patient outcomes, and costs. . Patients and Methods. The study was a prospective, randomized controlled trial of 50 patients undergoing TKA. There were 25 patients in each of the PSI and CSI groups. There were 12 male patients in the PSI group and seven male patients in the CSI group. The patients had a mean age of 69.0 years (. sd. 8.4) in the PSI group and 69.4 years (. sd. 8.4) in the CSI group. All patients received the same TKA implant. Intraoperative surgical resources and any surgical waste generated were recorded. Patients underwent radiostereometric analysis (RSA) studies to measure femoral and tibial component migration over two years. Outcome measures were recorded pre- and postoperatively. Overall costs were calculated for each group. Results. There were no differences (p > 0.05) in any measurement of migration at two years for either the tibial or femoral components. Movement between one and two years was < 0.2 mm, indicating stable fixation. There were no differences in coronal or sagittal alignment between the two groups. The PSI group took a mean 6.1 minutes longer (p = 0.04) and used a mean 3.4 less trays (p < 0.0001). Total waste generated was similar (10 kg) between the two groups. The PSI group cost a mean CAD$1787 more per case (p < 0.01). Conclusion. RSA criteria suggest that both groups will have revision rates of approximately 3% at five years. The advantages of PSI were minimal or absent for surgical resources used and waste eliminated, and for meeting target alignment, yet had significantly greater costs. Therefore, we conclude that PSI may not offer any advantage over CSI for routine primary TKA cases. Cite this article: Bone Joint J 2019;101-B:565–572

Aims. We conducted a randomised controlled trial to assess the accuracy of positioning and alignment of the components in total knee arthroplasty (TKA), comparing those undertaken using standard intramedullary cutting jigs and those with patient-specific instruments (PSI). Patients and Methods. There were 64 TKAs in the standard group and 69 in the PSI group. The post-operative hip-knee-ankle (HKA) angle and positioning was investigated using CT scans. Deviation of > 3° from the planned position was regarded as an outlier. The operating time, Oxford Knee Scores (OKS) and Short Form-12 (SF-12) scores were recorded. Results. There were 14 HKA-angle outliers (22%) in the standard group and nine (13%) in the PSI group (p = 0.251). The mean HKA-angle was 0.5° varus in the standard group and 0.2° varus in the PSI group (p = 0.492). The accuracy of alignment in the coronal and axial planes and the proportion of outliers was not different in the two groups. The femoral component was more flexed (p = 0.035) and there were significantly more tibial slope outliers (29% versus 13%) in the PSI group (p = 0.032). Operating time and the median three-month OKS were similar (p = 0.218 and p = 0.472, respectively). Physical and mental SF-12 scores were not significantly different at three months (p = 0.418 and p = 0.267, respectively) or at one year post-operatively (p = 0.114 and p = 0.569). The median one-year Oxford knee score was two points higher in the PSI group (p = 0.049). Conclusion. Compared with standard intramedullary jigs, the use of PSI did not significantly reduce the number of outliers or the mean operating time, nor did it clinically improve the accuracy of alignment or the median Oxford Knee Scores. Our data do not support the routine use of PSI when undertaking TKA. Cite this article: Bone Joint J 2016;98-B:1043–9

Introduction. The effectiveness of patient specific instrumentation (PSI) to perform total knee arthroplasty (TKA) remains controversial. Multiple studies have been published that reveal conflicting results on the effectiveness of PSI, but no study has analyzed the contact kinematics within knee joints replaced with the use of PSI. Since a departure from normal kinematics can lead to eccentric loading, premature wear, and component loosening, studying the kinematics in patients who have undergone TKA with PSI can provide valuable insight on the ability of PSI to improve functionality and increase longevity. The goal of the present study was to compare femoral and tibial component migration (predictive of long-term loosening and revision) and contact kinematics following TKA using conventional instruments (CI) and PSI based surgical techniques. Methods. The study was designed as a prospective, randomized controlled trial of 50 patients, with 25 patients each in the PSI and CI groups, powered for radiostereometric analysis (RSA). Patients in the PSI group received an MRI and standing 3-foot x-rays to construct patient-specific cut-through surgical guides for the femur and tibia with a mechanical limb alignment. All patients received the same posterior-stabilized implant with marker beads inserted in the bone around the implants to enable RSA imaging. Patients underwent supine RSA exams at multiple time points (two and six weeks, three and six months, and one and two years). At 2 years post-op, a series of RSA radiographs were acquired at different knee flexion angles, ranging in 20° increments from 0° to 120°, to measure the tibiofemoral contact kinematics. Migrations of the femoral and tibial components were calculated using model-based RSA software. Kinematics were measured for each condyle for magnitude of excursion, contact location, and stability. Results. There were no differences (p > 0.05) between the PSI and CI groups for demographics or pre- and post-operative patient reported outcome scores. Three patients in the PSI group and seven patients in the CI group (p = 0.28) had a post-operative limb alignment outside of the neutral target (>3° varus or valgus). There was no difference in the change of tibial slope from pre- to post-operation between groups (p = 0.49). There were no differences (p > 0.05) in translations or rotations in any individual plane across all time points for either the tibial or femoral components. Maximum total point motion (MTPM) at 6 months for the tibial component was 0.54 ± 0.25 mm in the CI group and 0.51 ± 0.22 mm in the PSI group (p = 0.77), placing both groups at the low end of the “at risk” category for predicted loosening. Change in MTPM from 6 months to 1 year and again from 1 year to 2 years was <0.2 mm, indicating both groups of implants had stable fixation. Femoral component MTPM was also not different (p > 0.05) between groups. There was no significant difference between PSI and CI groups with respect to magnitude of excursion on both medial (p = 0.54) and lateral (p = 0.81) condyles. There was also no difference in contact locations on both the medial and lateral condyles (p = 0.28 to 0.91) for all angles of flexion. There was no significant difference present between PSI and CI groups when comparing the stability for both the medial (p = 0.06) and lateral (= 0.85) condyles. Condylar separation was present in 3/20 CI patients and 0/16 PSI patients (p = 0.24). Conclusion. Using the latest RSA criteria for predicting failure from early migration, the use of PSI does not provide an advantage over CI for preventing aseptic loosening. Moreover, PSI did not provide any substantial advantage over CI for TKA surgery with respect to contact kinematics

We conducted a meta-analysis, including randomised controlled trials (RCTs) and cohort studies, to examine the effect of patient-specific instruments (PSI) on radiological outcomes after total knee replacement (TKR) including: mechanical axis alignment and malalignment of the femoral and tibial components in the coronal, sagittal and axial planes, at a threshold of > 3º from neutral. Relative risks (RR) for malalignment were determined for all studies and for RCTs and cohort studies separately. Of 325 studies initially identified, 16 met the eligibility criteria, including eight RCTs and eight cohort studies. There was no significant difference in the likelihood of mechanical axis malalignment with PSI versus conventional TKR across all studies (RR = 0.84, p = 0.304), in the RCTs (RR = 1.14, p = 0.445) or in the cohort studies (RR = 0.70, p = 0.289). The results for the alignment of the tibial component were significantly worse using PSI TKR than conventional TKR in the coronal and sagittal planes (RR = 1.75, p = 0.028; and RR = 1.34, p = 0.019, respectively, on pooled analysis). PSI TKR showed a significant advantage over conventional TKR for alignment of the femoral component in the coronal plane (RR = 0.65, p = 0.028 on pooled analysis), but not in the sagittal plane (RR = 1.12, p = 0.437). Axial alignment of the tibial (p = 0.460) and femoral components (p = 0.127) was not significantly different. We conclude that PSI does not improve the accuracy of alignment of the components in TKR compared with conventional instrumentation. Cite this article: Bone Joint J 2014; 96-B:1052–61

Improvements in the surgical technique of total knee replacement (TKR) are continually being sought. There has recently been interest in three-dimensional (3D) pre-operative planning using magnetic resonance imaging (MRI) and CT. The 3D images are increasingly used for the production of patient-specific models, surgical guides and custom-made implants for TKR. The users of patient-specific instrumentation (PSI) claim that they allow the optimum balance of technology and conventional surgery by reducing the complexity of conventional alignment and sizing tools. In this way the advantages of accuracy and precision claimed by computer navigation techniques are achieved without the disadvantages of additional intra-operative inventory, new skills or surgical time. This review describes the terminology used in this area and debates the advantages and disadvantages of PSI

Aims

Robotic arm-assisted surgery offers accurate and reproducible guidance in component positioning and assessment of soft-tissue tensioning during knee arthroplasty, but the feasibility and early outcomes when using this technology for revision surgery remain unknown. The objective of this study was to compare the outcomes of robotic arm-assisted revision of unicompartmental knee arthroplasty (UKA) to total knee arthroplasty (TKA) versus primary robotic arm-assisted TKA at short-term follow-up.

Aims

Intraoperative pressure sensors allow surgeons to quantify soft-tissue balance during total knee arthroplasty (TKA). The aim of this study was to determine whether using sensors to achieve soft-tissue balance was more effective than manual balancing in improving outcomes in TKA.

Aims

The impact of a diaphyseal femoral deformity on knee alignment varies according to its severity and localization. The aims of this study were to determine a method of assessing the impact of diaphyseal femoral deformities on knee alignment for the varus knee, and to evaluate the reliability and the reproducibility of this method in a large cohort of osteoarthritic patients.

Aims

A comprehensive classification for coronal lower limb alignment with predictive capabilities for knee balance would be beneficial in total knee arthroplasty (TKA). This paper describes the Coronal Plane Alignment of the Knee (CPAK) classification and examines its utility in preoperative soft tissue balance prediction, comparing kinematic alignment (KA) to mechanical alignment (MA).

Aims

The purpose of this study was to compare the radiological outcomes of manual versus robotic-assisted medial unicompartmental knee arthroplasty (UKA).

Aims

Patient-specific instrumentation of total knee arthroplasty (TKA) is a technique permitting the targeting of individual kinematic alignment, but deviation from a neutral mechanical axis may have implications on implant fixation and therefore survivorship. The primary objective of this randomized controlled study was to compare the fixation of tibial components implanted with patient-specific instrumentation targeting kinematic alignment (KA+PSI) versus components placed using computer-assisted surgery targeting neutral mechanical alignment (MA+CAS). Tibial component migration measured by radiostereometric analysis was the primary outcome measure (compared longitudinally between groups and to published acceptable thresholds). Secondary outcome measures were inducible displacement after one year and patient-reported outcome measures (PROMS) over two years. The secondary objective was to assess the relationship between alignment and both tibial component migration and inducible displacement.

Aims

The extensive variation in axial rotation of tibial components can lead to coronal plane malalignment. We analyzed the change in coronal alignment induced by tray malrotation.

Aims

This aim of this study was to assess the feasibility of designing and introducing generic 3D-printed instrumentation for routine use in total knee arthroplasty.

Total knee replacement (TKR) smart tibial trials have load-bearing sensors which will show quantitative compartment pressure values and femoral-tibial tracking patterns. Without smart trials, surgeons rely on feel and visual estimation of imbalance to determine if the knee is optimally balanced. Corrective soft-tissue releases are performed with minimal feedback as to what and how much should be released. The smart tibial trials demonstrate graphically where and how much imbalance is present, so that incremental releases can be performed. The smart tibial trials now also incorporate accelerometers which demonstrate the axial alignment. This now allows the surgeon the option to perform a slight recut of the tibia or femur to provide soft-tissue balance without performing soft-tissue releases. Using a smart tibial trial to assist with soft-tissue releases or bone re-cuts, improved patient outcomes have been demonstrated at one year in a multicentre study of 135 patients (135 knees).

Cite this article: Bone Joint J 2014;96-B(11 Suppl A):78–83.

In this study we randomised 140 patients who were due to undergo primary total knee arthroplasty (TKA) to have the procedure performed using either patient-specific cutting guides (PSCG) or conventional instrumentation (CI).

The primary outcome measure was the mechanical axis, as measured at three months on a standing long-leg radiograph by the hip–knee–ankle (HKA) angle. This was undertaken by an independent observer who was blinded to the instrumentation. Secondary outcome measures were component positioning, operating time, Knee Society and Oxford knee scores, blood loss and length of hospital stay.

A total of 126 patients (67 in the CI group and 59 in the PSCG group) had complete clinical and radiological data. There were 88 females and 52 males with a mean age of 69.3 years (47 to 84) and a mean BMI of 28.6 kg/m² (20.2 to 40.8). The mean HKA angle was 178.9° (172.5 to 183.4) in the CI group and 178.2° (172.4 to 183.4) in the PSCG group (p = 0.34). Outliers were identified in 22 of 67 knees (32.8%) in the CI group and 19 of 59 knees (32.2%) in the PSCG group (p = 0.99). There was no significant difference in the clinical results (p = 0.95 and 0.59, respectively). Operating time, blood loss and length of hospital stay were not significantly reduced (p = 0.09, 0.58 and 0.50, respectively) when using PSCG.

The use of PSCG in primary TKA did not reduce the proportion of outliers as measured by post-operative coronal alignment.

Cite this article: Bone Joint J 2015;97-B:56–63.

Objectives

Lower limb muscle power is thought to influence outcome following total knee replacement (TKR). Post-operative deficits in muscle strength are commonly reported, although not explained. We hypothesised that post-operative recovery of lower limb muscle power would be influenced by the number of satellite cells in the quadriceps muscle at time of surgery.

The purpose of this study was to test the hypothesis that patella alta leads to a less favourable situation in terms of patellofemoral contact force, contact area and contact pressure than the normal patellar position, and thereby gives rise to anterior knee pain.

A dynamic knee simulator system based on the Oxford rig and allowing six degrees of freedom was adapted in order to simulate and record the dynamic loads during a knee squat from 30° to 120° flexion under physiological conditions. Five different configurations were studied, with variable predetermined patellar heights.

The patellofemoral contact force increased with increasing knee flexion until contact occurred between the quadriceps tendon and the femoral trochlea, inducing load sharing. Patella alta caused a delay of this contact until deeper flexion. As a consequence, the maximal patellofemoral contact force and contact pressure increased significantly with increasing patellar height (p < 0.01). Patella alta was associated with the highest maximal patellofemoral contact force and contact pressure. When averaged across all flexion angles, a normal patellar position was associated with the lowest contact pressures.

Our results indicate that there is a biomechanical reason for anterior knee pain in patients with patella alta.