A novel patient-specific instrument design can deliver robotic level accuracy in unicompartmental knee arthroplasty

BackgroundA previous randomised controlled trial (RCT) by our group found that robotic assisted unicompartmental knee arthroplasty (UKA) surgery was significantly more accurate than conventional instrumentation. The aim of this study was to determine whether a low-cost novel PSI design could deliver the same level of accuracy as the robot in the same time efficient manner as conventional instruments.MethodsThirty patients undergoing medial UKA took part. Tibial component position was planned using a low dose CT-scan, and compared to a day 1 postoperative CT-scan to determine the difference between the planned and achieved positions. Operations were performed by one expert surgeon using PSI (Embody, London, UK).ResultsThe mean absolute difference between planned and achieved tibial implant positions using PSI was 2.0° (SD 1.0°) in the coronal plane, 1.8° (SD 1.5) in the sagittal plane, and 4.5° (SD 3.3) in the axial plane. These results were not significantly different to the 13 historical robotic cases (mean difference 0.5°, 0.5°, and 1.7°, p = 0.1907, 0.2867 and 0.1049 respectively). PSI mean operating time was on average 62 min shorter than the robotic group (p < 0.0001) and 40 min shorter than the conventional instrument group (p < 0.0001). No complications were reported.ConclusionsIn conclusion, this clinical trial demonstrates that for tibial component positioning in UKA, a novel design PSI guide in the hands of an expert surgeon, can safely deliver comparable accuracy to a robotic system, whilst being significantly faster than conventional instruments.NIHR Clinical Research Network Reference: 16100.     

Saw cuts in unicompartmental knee arthroplasty: An analysis of sawbone preparations

Unicompartmental knee arthroplasty (UKA) has become a frequently used treatment option for anteromedial osteoarthritis (OA) of the knee due to good clinical and functional results. However, serious complications like tibial plateau fractures have been reported. These can be associated with saw cuts during surgery. The purpose of this study was to analyse saw cuts during Sawbone^® preparations at instructional unicompartmental knee courses and to identify potential sources of surgical error. One hundred Sawbone^® preparations were performed by knee surgeons inexperienced with UKA. Sawing errors during preparation were analysed and quantified. Tibial and femoral errors can occur during preparation. At the proximal tibia three errors can be found: extended vertical cuts (A), extended horizontal cuts (B) and perforation of the posterior cortex. An ascending cut at the posterior femoral condyle (C) is possible during femoral preparation. Errors type A were found at a mean length of 2.4 mm ± 2.3 mm with a maximum value of 10.1 mm. In 18% errors of more than 4.0 mm were found. Type B errors showed an average value of 2.0 mm ± 1.7 mm with maximum values of 7.4 mm. Type C errors were found at a mean of 1.3 mm ± 1.0 mm (maximum value 5.1 mm). Our data showed that in 18% of the cases, vertical cutting errors of more than 4.0 mm occurred in inexperienced surgeons.     

术者经验对膝关节单髁置换术中的间隙平衡的影响：一项尸体研究

目的通过传感器技术,研究不同经验的术者在UKA术中所实现的间隙平衡是否有差别。方法依据术者既往单髁手术经验将术者分为无经验组、经验不足组及经验成熟组,通过压力传感器测量45例解冻尸体标本的单髁手术中的间隙压力,研究术者的手术经验是否与屈伸间隙平衡有关。结果经验成熟组术者的间隙平衡差为(53.19±43.47)N,显著低于经验不足组的(194.18±102.92)N和无经验组的(314.86±129.64)N(P<0.05)。而经验不足组与无经验组间差异无统计学意义(P>0.05)。结论术者的单髁手术经验与术中屈伸间隙平衡密切相关,而传感器技术可以帮助术者更加准确地判断间隙压力。     

Single photon emission computed tomography in planning unicompartmental knee arthroplasty. A prospective study examining the association between scan findings and intraoperative assessment of osteoarthritis

The aim of this study was to determine the relationship between preoperative single photon emission computed tomography (SPECT) scan findings and intraoperative assessments of knee osteoarthritis (OA) in patients undergoing tibiofemoral unicompartmental knee arthroplasty (UKA). Fifty knees in 46 patients undergoing UKA were investigated preoperatively with a SPECT scan to confirm unicompartmental disease. There were 38 men and 12 women in the cohort with an average age of 63 years (range 44-78). The SPECT scan uptake in each compartment of the knee was graded by a single radiologist and these findings were compared with intraoperative assessments of OA (size and grade of lesion), made by two experienced surgeons, blinded to the scan findings. Significant association was demonstrated between scan findings and OA in all compartments of the knee (p<0.05), and this was strongest in the medial compartment and weakest in the patellofemoral compartment and lateral tibial plateau. We conclude that SPECT scan is a useful imaging modality in the planning of medial tibiofemoral UKA to confirm unicompartmental disease. The lower degree of association between scan findings and OA encountered in the patellofemoral compartments and lateral tibial plateau indicates that greater vigilance should be exercised in the intraoperative assessment of these areas.     

Improvement of femoral component size prediction using a C-arm intensifier guide and our established algorithm in unicompartmental knee arthroplasty: A report from a Chinese population

BackgroundUnicompartmental knee arthroplasty (UKA) is becoming more widely used with the recent increase in popularity of the use of minimally invasive techniques. However, it is difficult to judge about the femoral component size in UKA using preoperative templating digitally or otherwise. Even when using navigation it is impossible to control the femoral component size. The aim of this study is to develop a better pre- or intra-operative measure that will predict femoral component size.MethodsNinety-two UKA cases were studied from June 2007 to December 2011 with a mean 26-month follow-up. We developed an intra-operative C-arm intensifier guide (CAIG) method for determining femoral size instead of pre-operative templating. The accuracy of prediction of both methods was compared from a review of post-operative radiographs. In addition, we summarized all cases and developed a Chinese algorithm to determine the femoral component size pre-operatively.ResultsThere was a significant difference between templating (59%) and CAIG (92%) method (P = 0.0001). In the Chinese algorithm, height based on gender and tibial size both have greater accuracy of prediction (88% and 70.7%) than the Oxford algorithm (51.1% and 59.8%). Component size distribution and optimal tibial/femoral pairing differed from those in the Oxford report.ConclusionsWe conclude that the Chinese algorithm can greatly improve the accuracy of prediction of femoral component size. In addition, CAIG-assisted implantation of a UKR is a reliable intra-operative tool and can aid size selection of the femoral component.Level of EvidenceLevel III.     

No difference in long-term outcomes between men and women undergoing medial fixed-bearing cemented unicompartmental knee arthroplasty: A retrospective cohort study with minimum 10-year follow up

BackgroundSome studies have suggested that women have poorer short-term outcomes after unicompartmental knee arthroplasty (UKA) due to a higher incidence of implant overhang. This study aimed to compare patient-reported outcome measures (PROMs) between men and women after UKA at a minimum follow-up of 10 years.MethodsPatients who underwent medial fixed-bearing UKA by two arthroplasty surgeons were identified from an institutional joint registry. Men and women were matched for age, body mass index, Charlson Comorbidity Index, American Society of Anesthesiologists class, range-of-motion and baseline PROMs using propensity scores. PROMs were compared at 2 and 10 years. Patients also completed a satisfaction questionnaire during these visits. Radiographic outliers were defined as > 2 mm of overhang.ResultsA total of 128 patients were included. There was no difference in complications, length of stay or readmissions. Women had poorer Knee Society functional scores, Short-Form 36 physical and mental component scores (SF-36 MCS) at 2 years. No difference in PROMs was found at 10 years, except for poorer SF-36 MCS in women (P = 0.041). At 10 years, 96% of women and 92% of men were satisfied (P = 0.243). Fifteen-year survivorship free from any revision was 96% in each group. There were more medial-tibial outliers in women (9%) compared with men (5%) (P = 0.018). However, no association between outliers and outcomes or survivorship was found on multivariate analyses.ConclusionThere was no difference in clinical outcomes between men and women undergoing UKA at a minimum follow-up of 10 years. While women had a higher incidence of medial tibial overhang, this was not associated with long-term outcomes or survivorship.     

Avoidance of intramedullary violation in computer-assisted total knee arthroplasty lowers the incidence of periprosthetic joint infection compared with conventional total knee arthroplasty: A propensity score matching analysis of 5342 cases

BackgroundConventional total knee arthroplasty (CONV-TKA) inevitably perturbs femoral medullary canal, disturbs medullary micro-architecture and increases blood loss and inflammatory responses. We hypothesized that avoidance of intramedullary violation may lower the incidence of periprosthetic joint infection (PJI). The aim of this study was to verify whether computer-assisted total knee arthroplasty (CAS-TKA) lowers the incidence of PJI as compared with CONV-TKA.MethodsA propensity score matching study of 5342 patients who underwent CAS-TKA (n = 1085) or CONV-TKA (n = 4257) for primary osteoarthritis of the knee from 2007 to 2015 in our institute was performed. Patients who underwent CAS-TKA were matched to those who received CONV-TKA at a 1:2 ratio according to demographics and comorbidities. PJI was defined according to the Musculoskeletal Infection Society diagnostic criteria from the 2013 International Consensus Meeting.ResultsAfter controlling potential risk factors, the use of CAS-TKA resulted in a lower incidence of PJI as compared with CONV-TKA [adjusted hazard ratio (HR), 0.42; 95% confidence interval (CI), 0.18–0.99]. The same trend in PJI reduction was observed with the usage of CAS-TKA under sensitivity testing [HR, 0.33; 95% CI, 0.12–0.95]. The cumulative incidence of PJI was lower in the CAS-TKA group than the CONV-TKA group (log-rank test, p = 0.013).ConclusionAvoidance of intramedullary violation during TKA may play a pivotal role in lowering the incidence of PJI. The use of CAS-TKA can reduce the incidence of PJI, with a better survival rate in terms of being free of PJI, as compared with CONV-TKA.Level of evidence III.     

No differences in patient-reported outcomes between medial pivot insert and symmetrical insert in total knee arthroplasty: A randomized analysis

Background

Although total knee arthroplasty (TKA) using a medial pivot insert reportedly improves kinematics compared with a symmetrical insert, improvements in patient-reported outcomes have not yet been reported. The aim of this study was to determine whether insert designs influenced patient-reported outcomes.

The use of pedobarographic analysis to evaluate movement patterns in unstable total knee arthroplasty: A proof of concept study

BackgroundDefinition and clinical diagnosis of instability in TKA is challenging. Sensitive and objective biomechanical tools to aid diagnosis are currently lacking. This proof-of-concept study evaluates the use of pressure mat analyses to identify abnormal biomechanical loading patterns associated with TKA instability within an outpatient clinical setting.MethodsTwenty participants were examined: 10 patients with suspected unilateral TKA instability and 10 healthy controls. Participants underwent bilateral stance and gait tests measuring time and limb loading pressure parameters. Gait was divided into three phases: heel strike, mid-foot and toe off. Pressure recordings are expressed relative to bodyweight. Between-limb loading discrepancies were calculated in TKA patients and controls, and these differences were then compared between groups. Statistical significance was accepted at p < 0.05.ResultsTKA patients consistently offloaded pressure away from the operated limb, whereas healthy controls exhibited more even limb loading throughout bilateral stance (p < 0.05). TKA patients exhibited greater discrepancy in overall step contact time between limbs (−0.09 s ± 0.16 s; p = 0.016) compared to controls (0.06 s ± 0.08 s; p = 0.04). Post-hoc tests showed significant between-group differences during midfoot (−0.04 s ± 0.07 s; p = 0.03) and toe-off (0.05 s ± 0.14 s; p = 0.013). Between-group differences in limb loading discrepancy were evident at heel strike (−9.24% ± 2.11%; p = 0.0166) and toe-off (−10.34% ± 5.51%; p = 0.0496).DiscussionPedobarographic measurements demonstrated differences in mechanical loading patterns in patients with TKA instability compared to healthy controls during functional tasks and warrants further investigation. This may prove to be a useful clinical diagnostic tool in identifying patients that would benefit from revision surgery or physical therapy.     

The role of the patellar tendon angle and patellar flexion angle in the interpretation of sagittal plane kinematics of the knee after knee arthroplasty: A modelling analysis

Background

Many different measures have been used to describe knee kinematics. This study investigated the changes of two measures, the patellar tendon angle and the patellar flexion angle, in response to variations in the geometry of the knee due to surgical technique or implant design.