Introduction

Robotic-arm assisted knee arthroplasty (rKA) has been associated with improved clinical, radiographic, and patient-reported outcomes. There is a paucity of literature, however, addressing its cost effectiveness. In the context of an integrated health system with an insurance plan and single source comprehensive data warehouse for electronic health records and claims data, we present an evaluation of healthcare costs and utilization associated with manual knee arthroplasty (mKA) versus rKA. We also examine the influence of rKA technology on surgeons’ practice patterns.

Joint load reduction is effective for alleviating OA pain. Treatment options for joint unloading include braces and HTO, both of which may be impractical for patients. The purpose of the present study was to examine the biomechanical rationale of a practical, partial unloading implant (KineSpring® System, Moximed) for knee OA.

Device durability was tested by cyclically loading bone-implant constructs through simulated use for at least 10 million cycles. Joint load reduction with the implant was quantified by measuring changes in medial and lateral knee compartment loads generated by cadaver knees in simulated gait. Safety of the device was tested by 3, 6, and 12 month follow-up of implants in an in vivo ovine model. Surgical technique and device safety and efficacy were assessed in human clinical studies.

The unloader device survived over 15 million cycles of simulated use without failure. In the simulated gait cadaver model, the unloading device significantly reduced medial compartment (29 ± 13 lbs, p<0.05) and overall knee joint loads during the stance phase of gait testing but did not significantly increase lateral compartment loading. Chronic ovine implants demonstrated good tolerance of the implant with normal wound healing and secure device fixation. Clinical experience (n=49) demonstrated uneventful device implantation. Unlike HTO, the implantation technique for the unloader does not alter joint alignment. This surgical technique avoids removal of bone, ligament, and cartilage, thus preserving future primary arthroplasty, if required. Early-term clinical experience also demonstrates good outcomes for patients, the earliest of whom are beyond 2.6 years with the implant.

This unloading device offers a practical and attractive treatment option for patients with medial knee OA: load reduction without load transfer, durability, preservation of downstream treatment options, safety, and early-term efficacy.

Joint load correlates with knee OA incidence, symptoms, radiographic, morphologic and biological changes. Available load modifying therapies are clinically effective but have drawbacks. The KineSpringTM (Moximed Inc), an investigational device, is designed to reduce compartment loads while avoiding the limitations of current treatments. We compare load reductions of braces, HTO and KineSpringTM.

Literature review and experimental data provide compartment load changes for clinically effective knee braces and HTO. Simulated gait testing was completed on four cadaver knees with early-stage OA. Gait was simulated using a cadaver-based kinematic test system that applies motion and loading patterns dynamically to cadaver specimens. Medial and lateral compartment femoro-tibial pressures were measured throughout testing using thin film dynamic pressure sensors (Tekscan, Inc.) placed inframeniscally. Three conditions were tested: no treatment, applied valgus moments to simulate a valgus moment brace, and implanted KineSpring.

Sufficient clinical data exists to support the development of new and novel load modifying therapies for knee OA. Joint load reductions provided by HTO and valgus moment braces provide insight into clinically effective load reduction ranges. Opening wedge HTOs of 5° and 10° are reported to reduce average medial compartment load by 55 N (12 lbs) and 286 N (64 lbs), respectively1. Valgus braces were reported to reduce medial compartment loads an average of 97-280 N (22-63 lbs). From this data we propose a clinically effective load reduction range of 55 to 286N is a valid indicator of the likely clinical success for medial knee load reduction treatments.

Gait simulation was successfully completed in all specimens in all test configurations. The valgus moment brace reduced medial compartment load by 58 ±20 N but did not reach statistical significance. The Kinespring reduced medial compartment load by 129±64 N in comparison to the untreated case, a statistically significant reduction. Neither the KineSpring nor the valgus moment brace caused significant changes in the lateral compartment during stance.

All treatments reduced medial compartment loads. KineSpringTM reduces loads in what we determined to be the clinically effective range. Additional studies and clinical investigations are warranted to determine the ultimate effectiveness of this implant system.

Introduction

Long bone surgery and marrow instrumentation represent significant surgical insults, and may cause severe local and systemic sequelae following both planned and emergent surgery. Preconditioning is a highly conserved evolutionary endogenous protective mechanism, but finding a clinically safe and acceptable method of induction has proven difficult. Glutamine, a known inducer of the heat shock protein (HSP) response, offers pharmacological modulation of injury through clinically acceptable preconditioning. This effect has not been previously demonstrated in an orthopaedic model.

Compartment syndrome (CS) is a unique form of skeletal muscle ischaemia. N-acetyl cysteine (NAC) is an anti-oxidant in clinical use, with beneficial microcirculatory effects.

Sprague-Dawley rats (n=6/group) were randomised into Control, CS and CS pre-treated with NAC (0.5g/kg i.p. 1 hr prior to induction) groups. In a post-treatment group NAC was administered upon muscle decompression. Cremasteric muscle was placed in a pressure chamber in which pressure was maintained at diastolic minus 10 mm Hg for 3 hours inducing CS, muscle was then returned to the abdominal cavity. At 24 hours and 7 days post-CS contractile function was assessed by electrical stimulation. Myeloperoxidase (MPO) activity was assessed at 24-hours.

CS injury reduced twitch (50.4±7.7 vs 108.5±11.5, p<0.001; 28.1±5.5 vs. 154.7±14.1, p<0.01) and tetanic contraction (225.7±21.6 vs 455.3±23.3, p<0.001; 59.7±12.1 vs 362.9±37.2, p<0.01) compared with control at 24 hrs and 7 days respectively. NAC pre-treatment reduced CS injury at 24 hours, preserving twitch (134.3±10.4, p<0.01 vs CS) and tetanic (408.3±34.3, p<0.01 vs CS) contraction. NAC administration reduced neutrophil infiltration (MPO) at 24 hours (24.6±5.4 vs 24.6±5.4, p<0.01). NAC protection was maintained at 7 days, preserving twitch (118.2±22.9 vs 28.1±5.5, p<0.01) and tetanic contraction (256.3±37 vs 59.7±12.1, p<0.01). Administration of NAC at decompression also preserved muscle twitch (402.4±52; p<0.01 versus CS) and tetanic (402.4±52; p<0.01 versus CS) contraction, reducing neutrophil infiltration (24.6±5.4 units/g; p<0.01).

These data demonstrate NAC provided effective protection to skeletal muscle from CS induced injury when given as a pre- or post-decompression treatment.