Tracy L. Kinsey

Overhang of the Femoral Component in Total Knee Arthroplasty: Risk Factors and Clinical Consequences

BACKGROUND Recently, much attention has been directed to femoral component overhang in total knee arthroplasty. The purposes of this study were to describe the prevalence of femoral component overhang among men and women after total knee arthroplasty, to identify risk factors for overhang, and to determine whether overhang was associated with postoperative knee pain or decreased range of motion. METHODS Femoral component overhang was measured intraoperatively during 437 implantations of the same type of total knee arthroplasty prosthesis. The overhang of metal beyond the bone cut edge was measured in millimeters at the midpoint of ten zones after permanent fixation of the implant. Factors predictive of overhanging fit were identified, and the effect of overhang on postoperative pain and flexion was examined. RESULTS Overhang of >or=3 mm occurred in at least one zone among 40% (seventy-one) of 176 knees in men and 68% (177) of 261 knees in women, most frequently in lateral zones 2 (anterior-distal) and 3 (distal). Female sex, shorter height, and larger femoral component size were highly predictive of greater overhang in multivariate models. Femoral component overhang of >or=3 mm in at least one zone was associated with an almost twofold increased risk of knee pain more severe than occasional or mild at two years after surgery (odds ratio, 1.9; 95% confidence interval, 1.1 to 3.3). CONCLUSIONS In this series, overhang of the femoral component was highly prevalent, occurring more often and with greater severity in women, and the prevalence and magnitude of overhang increased with larger femoral component sizes among both sexes. Femoral component overhang of >or=3 mm approximately doubles the odds of clinically important knee pain two years after total knee arthroplasty.

Correlation Between Muscle Oxygenation and Compartment Pressures in Acute Compartment Syndrome of the Leg

BACKGROUND Near-infrared spectroscopy estimates soft-tissue oxygenation approximately 2 to 3 cm below the skin. The purpose of the present study was to evaluate muscle oxygenation in the setting of an acute compartment syndrome of the leg and to determine if near-infrared spectroscopy is capable of detecting perfusion deficits. METHODS Fourteen patients with unilateral lower extremity trauma were enrolled after the diagnosis of an acute compartment syndrome was made clinically and confirmed with intracompartmental pressure measurements. Lower extremity muscle compartments were evaluated with near-infrared spectroscopy, and near-infrared spectroscopy values of the uninjured, contralateral leg of each patient were used as internal reference values. The compartment perfusion gradient was calculated as the diastolic blood pressure minus the intracompartmental pressure. RESULTS Intracompartmental pressures ranged from 21 to 176 mm Hg (mean, 79 mm Hg) and exceeded 30 mm Hg in all compartments but two (both in the same patient). Thirty-eight compartments had a perfusion gradient of < or = 10 mm Hg (indicating ischemia). Among ischemic compartments, near-infrared spectroscopy values in the anterior, lateral, deep posterior, and superficial posterior compartments of the injured limbs were decreased by an average 10.1%, 10.1%, 9.4%, and 16.3% in comparison with the corresponding compartments of the uninjured leg. Differences in near-infrared spectroscopy values (the near-infrared spectroscopy value for the injured leg minus the near-infrared spectroscopy value for the uninjured leg) were positively correlated with compartment perfusion gradient within each compartment (r = 0.82, 0.65, 0.67, and 0.62, for the anterior, lateral, deep posterior, and superficial posterior compartments, respectively; p < 0.05 for all). CONCLUSIONS Normalized near-infrared spectroscopy values decrease significantly with decreasing lower limb perfusion pressures. Near-infrared spectroscopy may be capable of differentiating between injured patients with and without an acute compartment syndrome.

Near-infrared spectroscopy in lower extremity trauma.

BACKGROUND Near-infrared spectroscopy measures the percentage of hemoglobin oxygen saturation in the microcirculation of tissue up to 3 cm below the skin. The purpose of this study was to describe the measurable response of normal tissue oxygenation in the leg after acute trauma with use of this technique. METHODS Twenty-six patients with acute unilateral tibial fractures and twenty-five uninjured volunteer control subjects were enrolled. Near-infrared spectroscopy measurements were obtained for both legs in all four compartments: anterior, lateral, deep posterior, and superficial posterior. The twenty-six injured legs were compared with twenty-five uninjured legs (randomly selected) of the volunteer control group, with the contralateral limb in each patient serving as an internal control. RESULTS The mean tissue oxygenation for each compartment in the injured legs was 69% (anterior), 70% (lateral), 74% (deep posterior), and 70% (superficial posterior). In the control (uninjured) legs, the average tissue oxygenation percentage in each compartment was 54%, 55%, 60%, and 57%, respectively. Repeated-measures analysis revealed that near-infrared spectroscopy values averaged 15.4 percentage points (95% confidence interval, 12.2 to 18.6 percentage points) higher for injured legs than for uninjured legs, controlling for the value of the contralateral limb (p < 0.0001). CONCLUSIONS Tibial fracture produces a predictable increase in tissue oxygenation as measured by near-infrared spectroscopy. The corresponding compartment of the contralateral leg can provide strong utility as an internal control value when evaluating the hyperemic response to injury.

Modular femoral offset stems facilitate joint line restoration in revision knee arthroplasty.

Restoration of proper joint line position in revision total knee arthroplasty is essential in promoting recovery of function. We retrospectively analyzed joint line restoration and clinical outcomes in 22 consecutive femur revision cases using modular offsets of variable length and direction between the intramedullary fixation rod and the femoral component. Flexion and extension gap balancing techniques and medial epicondylar referencing was used to achieve proper position of the joint line. Position of the reconstructed joint line from postoperative radiographs was compared to the baseline position of intended anatomic placement determined from pre-operative planning radiographs. Postoperative joint line height averaged 1.6 mm distal to baseline (range, 5 mm distal to 2.5 proximal). Joint line was restored to within 2 mm of anatomic position in 12 of the 22 knees. Sixteen patients received conventional, minimally constrained tibial inserts, and joint stability was achieved in all cases.Level of Evidence: Therapeutic study, Level IV (case series). See Guidelines for Authors for a complete description of levels of evidence.

The New Arthritic Patient and Arthroplasty Treatment Options

• Describe the indications for unicompartmental femorotibial knee arthroplasty • Describe the key technical points during surgery for patellofemoral replacement.

Can Squeaking With Ceramic-On-Ceramic Hip Articulations In Total Hip Arthroplasty Be Avoided?

Squeaking is a recognized complication of total hip arthroplasty with ceramic on ceramic bearings but the etiology has not been well identified. We evaluated 183 hips in 148 patients who had undergone ceramic-on-ceramic noncemented total hip arthroplasties at one center between 1997-2007 by standardized telephone interviews and radiographic review. Audible squeaking was reported from 22 hips (12% of 183) of 19 patients. Prevalence of squeaking was associated with younger age; obesity; lateralized cup position; use of beta titanium alloy femoral components and shortened head length options; and higher reported activity level, greater pain, and decreased satisfaction at the time of the interview. Squeaking was described as having little personal significance by most patients. Squeaking might be preventable in part through medialization of the acetabular cup and avoidance of the use of shortened femoral necks.

Biomechanical influence of TKA designs with varying radii on bilateral TKA patients during sit-to-stand

BackgroundCompared to the design of a traditional multi-radius (MR) total knee arthroplasty (TKA), the single-radius (SR) implant investigated has a fixed flexion/extension center of rotation. The biomechanical effectiveness of an SR for functional daily activities, i.e., sit-to-stand, is not well understood. The purpose of the study was to compare the biomechanics underlying functional performance of the sit-to-stand (STS) movement between the limbs containing an MR and an SR TKA of bilateral TKA participants.MethodsSagittal plane kinematics and kinetics, and EMG data for selected knee flexor and extensor muscles were analyzed for eight bilateral TKA patients, each with an SR and an MR TKA implant.ResultsCompared to the MR limb, the SR limb demonstrated greater peak antero-posterior (AP) ground reaction force, higher AP ground reaction impulse, less vastus lateralis and semitendinosus EMG during the forward-thrust phase of the STS movement. No significant difference of knee extensor moment was found between the two knees.ConclusionSome GRF and EMG differences were evident between the MR and SR limbs during STS movement. Compensatory adaptations may be used to perform the STS.

Difference in Hip Prosthesis Femoral Offset Affects Hip Abductor Strength and Gait Characteristics During Obstacle Crossing

The purpose of this article is to determine if individuals with high rather than low femoral offset of a total hip arthroplasty achieve improved hip abductor muscle strength and thus improved their ability to step over an obstacle safely. These outcomes will help surgeons decide whether increasing the femoral offset helps a patients physical function.

Rotational Kinematics of a Modern Fixed-Bearing Posterior Stabilized Total Knee Arthroplasty

The purpose of this study was to evaluate the rotational kinematics of a fixed-bearing posteriorly stabilized total knee design in moderate and deep flexion. Three-dimensional kinematics analyses were conducted on 20 knees in 4 weight-bearing positions using 3-dimensional shape-matching techniques. Average maximum skeletal flexion was 138 degrees . Internal tibial rotation was demonstrated in 19 of 20 knees. The average internal tibial rotation in midflexed lunge was 5.5 degrees (-3.8 degrees to 14.1 degrees ) and in maximum flexion kneeling was 4.0 degrees (-3.1 degrees to 10.6 degrees ). Separation of articular surfaces was not identified. In this study, patients with this device demonstrated patterns of rotation similar to those previously reported for both the normal knee and rotating platform designs.

Relationship between Near Infrared Spectroscopy and Intra-compartmental Pressures

BACKGROUND Near infrared spectroscopy (NIRS) has been suggested as a possible means for detecting perfusion deficits in patients with acute compartment syndrome (ACS). STUDY OBJECTIVES To longitudinally examine NIRS in an ACS model to determine its responsiveness to decreasing perfusion pressure. METHODS A NIRS sensor pad was placed under a tourniquet over the anterior compartment in the mid-tibia region on 20 volunteers. Initial perfusion pressures and NIRS values were recorded. The tourniquet pressure was sequentially raised by 10 mm Hg in 10-min intervals until systolic pressure was surpassed. NIRS values and perfusion pressure were determined at the end of each 10-min interval. RESULTS There was no change in mean NIRS values from the initial baseline until 30 mm Hg of perfusion pressure was reached. Additionally, a statistically significant drop in mean NIRS values was observed as perfusion pressures dropped from 10 mm Hg to 0 mm Hg, and again with subsequent decreases of 10 mm Hg perfusion pressure until systolic pressure was surpassed. CONCLUSIONS These results coincide with previously published studies using alternative methods of measuring blood flow or perfusion. NIRS values were responsive to decreasing perfusion pressures over a longitudinal period of time in an ACS model. These results suggest that NIRS may be useful for continuous, non-invasive monitoring of patients for whom ACS is a concern. Additional studies on traumatized patients are required.