There is strong current interest to provide reliable treatments for one- and two-compartment arthritis in the cruciate-ligament intact knee. An alternative to total knee arthroplasty is to resurface only the diseased compartments with discrete compartmental components. Placing multiple small implants into the knee presents a greater surgical challenge than total knee arthroplasty, and it is not certain natural knee mechanics can be maintained. The goal of this study was to compare functional kinematics in cruciate-intact knees with either medial unicondylar (mUKA), mUKA plus patellofemoral (mUKA+PF), or bi-unicondylar (biUNI) arthroplasty using discrete compartmental implants with preparation and placement assisted by haptic robotic technology. Nineteen patients with 21 knee arthroplasties consented to participate in an I.R.B. approved study of knee kinematics with a cruciate-retaining multicompartmental knee arthroplasty system. All subjects presented with knee OA, intact cruciate ligaments, and coronal deformity ranging from 7° varus to 4° valgus. All subjects received multicompartmental knee arthroplasty using haptic robotic-assisted bone preparation an average of 13 months (6–29 months) before the study. Eleven subjects received mUKA, five subjects received mUKA+PF, and five subjects received biUKA. Subjects averaged 62 years of age and had an average body mass index of 31. Combined Knee Society Pain/Function scores averaged 102 ± 28 preoperatively and 169 ± 26 at the time of study. Knee range of motion averaged −3° to 120° preoperatively and −1° to 129° at the time of the study. Knee motions were recorded using video-fluoroscopy while subjects performed step-up/down, kneeling and lunging activities. The three-dimensional position and orientation of the implant components were determined using model-image registration techniques (Fig. 1). The AP locations of the medial and lateral condyles were determined by computing a distance map between the femoral condyles and the tibial articular surfaces.INTRODUCTION
METHODS
There is great interest to provide repeatable and durable treatments for arthritis localized to one or two compartments in the cruciate-ligament intact knee. We report a series of efforts to develop and characterize an implant system for partial knee resurfacing. We studied distal femoral morphology and found that the sagittal-plane relationships between the condylar and trochlear surfaces are highly variable (Figs 1 and 2). In response, we report the design of a multi-compartmental system of implants intended to anatomically resurface any combination of compartments (Fig 3). Finally, we report the results of a pilot fluoroscopic study of the in vivo knee kinematics in patients who received medial, medial plus patellofemoral and bi-condylar knee arthroplasty. The kinematic results suggest these treatments provide a stable knee with intact cruciate ligament function. This work shows various partial knee resurfacing treatments have the potential to provide excellent knee mechanics and clinical outcomes.
The advantages of the direct anterior approach (DAA) for total hip arthroplasty include the preservation of external rotators and hip abductors thus leading to quicker recovery times. To our knowledge, there is no objective method in the literature to predict the level of difficulty for femoral exposure through the DAA. It would be beneficial to the surgeon learning the DAA to assess difficulty pre-operatively to avoid prolonged operative times. The purpose of this study was to develop a predictive model of femoral exposure difficulty in the DAA using a combination of demographic data and radiographic measurements. 305 post-operative radiographs of consecutive THA's in patients (184 female, 120 male) with primary or secondary osteoarthritis, mean age 64.6 (range 26–91, SD=11.43) performed through the DAA by one of the co-investigators from 12/2005 to 12/2009 were retrospectively reviewed by two separate observers. The observers were blinded to the difficulty level of femoral exposure. Standard post-operative AP pelvis films were assessed with TraumaCad software (TraumaCad 2.2, Voyant Health, Columbia, MD) to make radiographic measurements as shown in Figure 1–2. Each radiograph was calibrated using the size of the femoral head implant. Exclusion criteria included films that had inadequate coverage of the entire pelvis, mal-rotation, or poor exposure. Statistical analysis was performed using STAT 9.1 (StatCorp; College Station, Texas, USA). A two-sided Kruskal–Wallis test was utilized for non-parametric data. Chi-squared tests and Fisher's Exact Test were used to compare proportions. Statistically significant associations were then added to a multivariate model predicting an outcome of difficult exposure.Introduction
Methods
Total knee arthroplasty is traditionally performed using bone anatomy to dictate femoral implant rotation and soft tissue release to balance any resulting deficiencies. A force sensing device has been developed that reverses this conventional order. It measures the forces in the medial and lateral compartments and dictates the femoral rotation cuts when these are equal. The purpose of this study was to compare the traditional methods of femoral rotation (TEA, AP axis, and posterior referenced) to this novel approach using computer navigation with the force sensor to determine a balanced flexion gap. This was a prospective cohort study of 50 consecutive primary TKA's. Inclusion criteria were diagnosis of OA and primary TKA. Exclusion criteria were inability to use force sensing device. The cohort consisted of 29 females and 19 males with an average age of 70.8 years (50.2-90.3) and BMI of 32.0 (19.8 – 56.1). Intra-operative data was collected using computer navigation. Post operative CT scans were obtained on 31 of the 50 knees to assess femoral implant rotation to the patients' true TEA. CT measurements were made by two different observers. Simple descriptive statistics and t-tests were used for analysis.Introduction
Methods
The incorporation of computer navigation in total hip arthroplasty (THA) has been much slower then for total knee arthroplasty (TKA). Computer navigation has proven itself in the realm of TKA but still has yet to advance in THA. The reasons for this include the lack of ease of incorporation, accuracy and precision, and the addition of overall operative time. Another reason for this lack of progress is that a majority of THA's are done with the patient in the lateral position through a posterior or lateral approach making the tracker placement and the registration process somewhat cumbersome. In the direct anterior approach the patient is in the supine position, which accommodates pelvic tracker placement and significantly facilitates the registration process. At our institution we use the direct anterior approach and computer navigation on all of our primary THA's. We hypothesized that computer navigation facilitates cup placement and leg length determination with out significantly increasing our operative time. This was a prospective study comparing a consecutive series of 150 computer navigated total hips to a consecutive series of 150 none navigated total hips. The two groups were similar by age, sex, and BMI. Operative times were collected using our secure online database. The start and stop of operative time was incision to final reduction respectively. Post operative radiographs were analyzed using TraumaCad 2.0 (Voyant Health, Columbia, MD). Cup angle and leg length were measured on A/P pelvic views. Simple descriptive statistics and t-tests were used to analyze data.Introduction
Materials and Methods
