Designing a Rational Follow-Up Schedule for Patients with Extremity Soft Tissue Sarcoma.

PURPOSE: The risk of tumor recurrence after resection of soft tissue sarcoma (STS) necessitates surveillance in follow-up. The objective of this study was to determine the frequency/timing of metastasis and local recurrence following treatment for soft tissue sarcoma, and to use these data to justify an evidence-based follow-up schedule. METHODS: Utilizing a prospective database, a retrospective single center review was performed of all patients with minimum 2-year follow-up after resection of a localized extremity STS. Kaplan-Meier estimates were used to calculate the incidence of local recurrence and metastases on an annual basis for 10 years. RESULTS: We identified a total of 230 low-grade, 626 intermediate-grade and 940 high-grade extremity STS and a total of 721 events, 150 local recurrences and 571 metastases. Based on tumor size and grade, follow-up cohorts were developed that had similar metastatic risk. Using pre-determined thresholds for metastatic event, a follow-up schedule was established for each cohort. CONCLUSION: Based on our results we recommend that patients with small low-grade tumors undergo annual follow-up for 5 years following definitive local treatment. Patients with large low-grade tumors, small intermediate-grade and small high-grade tumors should have follow-up every 6 months for the first 2 years, then yearly to 10 years. Only patients with large intermediate- or high-grade tumors require follow-up every 3 months for the first 2 years, then every 6 months for years 3-5, followed by annually until 10 years.

Validation of three-dimensional models of the distal femur created from surgical navigation point cloud data for intraoperative and postoperative analysis of total knee arthroplasty.

PURPOSE: Despite the success of total knee arthroplasty, there continues to be a significant proportion of patients who are dissatisfied. One explanation may be a shape mismatch between pre- and postoperative distal femurs. The purpose of this study was to investigate methods suitable for matching a statistical shape model (SSM) to intraoperatively acquired point cloud data from a surgical navigation system and to validate these against the preoperative magnetic resonance imaging (MRI) data from the same patients. METHODS: A total of 10 patients who underwent navigated total knee arthroplasty also had an MRI scan <2 months preoperatively. The standard surgical protocol was followed which included partial digitization of the distal femur. Two different methods were employed to fit the SSM to the digitized point cloud data, based on (1) iterative closest points and (2) Gaussian mixture models. The available MRI data were manually segmented and the reconstructed three-dimensional surfaces used as ground truth against which the SSM fit was compared. RESULTS: For both approaches, the difference between the SSM-generated femur and the surface generated from MRI segmentation averaged less than 1.7 mm, with maximum errors occurring in less clinically important areas. CONCLUSION: The results demonstrated good correspondence with the distal femoral morphology even in cases of sparse datasets. Application of this technique will allow for measurement of mismatch between pre- and postoperative femurs retrospectively on any case done using the surgical navigation system and could be integrated into the surgical navigation unit to provide real-time feedback.

Changes in the functional flexion axis of the knee before and after total knee arthroplasty using a navigation system.

Long term satisfaction of patients with total knee arthroplasty (TKA) has lagged behind that of total hip arthroplasty. One possible reason is the failure of the artificial joint to recreate natural kinematics of the knee. This study evaluated the pre and post implant functional flexion axis in the knees of 285 total knee arthroplasty patients using a surgical navigation system. Results showed that post-implant there was less femoral rollback early in flexion on the lateral side of the joint than pre-implant. Designing future generations of knee implants to allow for this motion may give patients a more 'natural' feeling knee and may benefit outcomes.

Pre-operative muscle activation patterns during walking are associated with TKA tibial implant migration.

BACKGROUND: Gait biomechanical variables have been associated with total knee arthroplasty tibial implant migration measured with Radiostereometric Analysis (RSA), but no studies have examined the role of the periarticular musculature, which is responsible for a high proportion of the forces on the joint. The purpose of this study was to measure the pre-operative electromyography (EMG) patterns of the periarticular knee muscles during gait and determine the association of these patterns with the post-operative tibial implant migration measured with RSA. We hypothesized that pre-operative muscle activation patterns (specifically the activation patterns of the vastus and gastrocnemius muscle groups) measured with EMG are associated with migration at 6months. METHODS: Electromyographic data were collected from 6 periarticular knee joint muscles on 37 patients pre-operatively during gait. Radiostereometric exams were performed immediately and at 6 months post-operatively. Relationships between the pre-operative patterns of muscle activation and micromotion of the implant were examined using Pearson correlation and regression models. FINDINGS: Statistically significant correlations were found between the pattern of the quadriceps and gastrocnemius muscle activations during gait and implant translation in the posterior direction. Regression analysis illustrated that a substantial proportion of the variance in the post-operative tibial component posterior translation (R2=0.49) was explained by a prolonged activation of the vastus medialis muscle and higher activation of the lateral gastrocnemius muscle during early stance. INTERPRETATION: The variability in migration explained by the muscle activation patterns supports the hypothesis that pre-operative functional characteristics can contribute to predicting implant migration following total knee arthroplasty surgery.

The knee adduction moment during gait is associated with the adduction angle measured during computer-assisted total knee arthroplasty.

Computer-assisted surgery can be used to measure 3-dimensional knee function during arthroplasty surgery; however, it is unknown if the movement of the knee measured during surgery is related to the in vitro, dynamic state of the knee joint, specifically the knee adduction moment during gait, which has been related to implant migration. The purpose of this study was to determine if the preoperative adduction moment is correlated with the knee abduction/adduction angle measured intraoperatively. A statistically significant correlation was found between the mean (r(2) = 0.59; P = .001) and peak (r(2) = 0.53; P = .003) preoperative knee adduction moment and the mean abduction/adduction angle measured intraoperatively. The association found in this study suggests the potential for incorporating functional information that relates to surgical outcome into surgical decision making using computer-assisted surgery.

Early failure of a polyethylene acetabular liner cemented into a metal cup.

In 2002, a patient underwent revision total hip arthroplasty for polyethylene wear. The acetabular cup was well fixed, and it was decided to cement a new polyethylene liner into the existing cup. In 2006, the patient presented with inability to weight bear and easy subluxation of the hip. Revision surgery was performed, and all components were examined postoperatively. Investigation with microcomputed tomography revealed that the liner had plastically deformed at the superior pole resulting in the hip instability. The reasons for this are suspected to be related to the abducted nature of the original cup and an uneven cement mantle. This report suggests that cementation of polyethylene liners into metal cups has limitations and is not appropriate in all circumstances.

Continued stabilization of trabecular metal tibial monoblock total knee arthroplasty components at 5 years-measured with radiostereometric analysis.

BACKGROUND AND PURPOSE: The trabecular metal tibial monoblock component (TM) is a relatively new option available for total knee arthroplasty. We have previously reported a large degree of early migration of the trabecular metal component in a subset of patients. These implants all appeared to stabilize at 2 years. We now present 5-year RSA results of the TM and compare them with those of the NexGen Option Stemmed cemented tibial component (Zimmer, Warsaw IN). PATIENTS AND METHODS: 70 patients with osteoarthritis were randomized to receive either the TM implant or the cemented component. RSA examination was done postoperatively and at 6 months, 1 year, 2 years, and 5 years. RSA outcomes were translations, rotations, and maximum total point motion (MTPM) of the components. MTPM values were used to classify implants as "at risk" or "stable". RESULTS: At the 5-year follow-up, 45 patients were available for analysis. There were 27 in the TM group and 18 in the cemented group. MTPM values were similar in the 2 groups (p = 0.9). The TM components had significantly greater subsidence than the cemented components (p = 0.001). The proportion of "at risk" components at 5 years was 2 of 18 in the cemented group and 0 of 27 in the TM group (p = 0.2). INTERPRETATION: In the previous 2-year report, we expressed our uncertainty concerning the long-term stability of the TM implant due to the high initial migration seen in some cases. Here, we report stability of this implant up to 5 years in all cases. The implant appears to achieve solid fixation despite high levels of migration initially.

Preoperative gait patterns and BMI are associated with tibial component migration.

BACKGROUND AND PURPOSE: There is no standard for patient triage in total knee arthroplasty (TKA) based on joint functional characteristics. This is largely due to the lack of objective postoperative measurement of success in TKA in terms of function and longevity, and the lack of knowledge of preoperative metrics that influence outcome. We examined the association between the preoperative mechanical environment of the patients knee joint during gait and the post-TKA stability of the tibial component as measured with radiostereometric analysis (RSA). METHODS: 37 subjects were recruited out of a larger randomized RSA trial. 3-dimensional gait analysis was performed in the preoperative week. Longitudinal RSA data were gathered postoperatively at 6 months and 1 year. RESULTS: We found a statistically significant association between the pattern of the knee adduction moment during gait preoperatively and the total migration of the implant at 6 months postoperatively. A substantial proportion of the variability in the total postoperative tibial component migration (R(2) = 0.45) was explained by a combination of implant type, preoperative knee joint loading patterns during gait, and body mass index at 6 months postoperatively. The relationships did not remain statistically significant at 1 year postoperatively. INTERPRETATION: Our findings support the hypothesis that preoperative functional characteristics of patients, and particularly joint loading patterns during activities of daily living, are important for outcome in TKA. This represents a first step in the development of predictive models of objective TKA outcome based on preoperative patient characteristics, which may lead to better treatment strategies. ClinicalTrials.gov (NCT00405379).

Inducible displacement of a trabecular metal tibial monoblock component.

Radiostereometric analysis is a highly accurate technique that can be used for measuring micromotion at the bone-implant interface. The purpose of this study was to compare the inducible displacement of the uncemented Trabecular Metal (TM; Zimmer, Warsaw, Ind) tibial monoblock component with that of a cemented implant. Inducible displacement of 14 uncemented TM components and 11 cemented components was measured 24 to 48 months postoperatively. Longitudinal migration of the implants was also measured with radiostereometric analysis at 6, 12, and 24 months postoperatively. The uncemented TM group had significantly lower inducible displacement than the cemented components. Significant correlations were found between longitudinal migration and the inducible displacement tests. The low values of inducible displacement in the TM group indicated good fixation and a promising long-term prognosis.