We introduce a novel active tensioning system that can be used for dynamic gap-based implant planning as well as for assessment of final soft tissue balance during implant trialing. We report on the concept development and preliminary findings observed during early feasibility testing in cadavers with two prototype systems. The active spacer (fig 1) consists of a motorized actuator unit with integrated force sensors, independently actuated medial and lateral upper arms, and a set of modular attachments for replicating the range of tibial baseplate and insert trial sizes. The spacer can be controlled in either force or position (gap) control and is integrated into the OMNIBoticsTM Robotic-assisted TKA platform (OMNI, MA, USA). Two design iterations were evaluated on eleven cadaver specimens by seven orthopaedic surgeons in three separate cadaver labs. The active spacer was used in a tibial-first technique to apply loads and measure gaps prior to and after femoral resections. To determine the range of forces applied on the spacer during a varus/valgus assessment procedure, each surgeon performed a varus/valgus stress test and peak medial and lateral forces were measured. Surgeons also rated the feel of the stability of the knee at 50N and 80N of preload using the following scale: 1 – too loose; 2 – slightly loose; 3 – ideal; 4 slightly tight; 5 – too tight. Final balanced was assessed with the spacer and with manual trial components.System description
Cadaver Study
Total hip arthroplasty has become an increasingly common procedure. Improper cup position contributes to bearing surface wear, pelvic osteolysis, dislocations, and revision surgery. The incidence of cup malposition outside of the safe zone (40° ± 10° abduction and 15° ± 10° anteversion) using traditional techniques has been reported to be as high as 50%. Our hypothesis is that computer assisted navigation will improve cup placement in total hip arthroplasty compared with traditional techniques. This study retrospectively evaluated the position of 425 consecutive cups placed during primary total hip arthroplasty performed over a two-year period, from 8/1/2012 to 8/1/2014. All cups were placed with a direct-anterior muscle-sparing approach with computer-assisted imageless navigation by a single surgeon. Real-time intraoperative “screen shots” were taken of cup placement. Standard antero-posterior postoperative radiographs of the pelvis were taken within 6 weeks of surgery in the operating surgeon's office using the same standardized protocol for each patient. The radiographs were evaluated by two separate investigators for final abduction and anteversion utilizing the same method as other studies. Statistics were descriptive in nature.Introduction
Methods
The aim of this study was to assess the outcome of patients who underwent ElmslieTrillat antero-medial tibial tubercle transfer for treatment of persistent symptomatic anterior knee pain due to chondromalacia patellae. We performed a prospective analysis of 23 patients who underwent Elmslie-Trillat antero-medial tibial tubercle transfers over a five year period for chronic anterior knee pain and an arthroscopic diagnosis of chondromalacia patellae. All patients who presented with anterior knee pain underwent an initial period of physiotherapy and all patients whose symptoms persisted following physiotherapy underwent arthroscopic assessment. Patients who continued to experience debilitating symptoms despite this initial treatment and who also had a diagnosis of chondromalacia patellae from arthroscopic assessment were listed for an Elmslie-Trillat tibial tubercle anteromedialisation. Patients who gave a history of instability or dislocation were excluded. The average age of patients undergoing surgery was 34 years (21–48 years) and the average time between arthroscopic diagnosis and surgery was 14 months. All patients who underwent surgery had pre and post operative KuJala patellofemoral scoring. The average pre-operative score was 54 (30–78) and post operative score 76 (46–100). The average post operative assessment was 25 months (6–62 months). Twenty one patients had improved post operative scores with one having a worse score and one score remaining unchanged following surgery. Nineteen patients felt that their symptoms had improved, three felt that there had been no change and one felt that they were worse after surgery. When asked if the improvement in symptoms had been worthwhile nineteen stated that they would undergo surgery again if in the same situation and four stated that they would not. The treatment of symptomatic chondromalacia patellae remains a challenge. Although a more selective approach to individuals with anterior knee pain is widely advocated in the literature this study demonstrates that good results can still be achieved in patients treated empirically with a tibial tubercle anteromedialisation.
