Bryan T. Leek

Noninvasive measurements of intramuscular pressure using pulsed phase-locked loop ultrasound for detecting compartment syndromes: a preliminary report.

Objectives To develop a human model for compartment tamponade and test the efficacy of ultrasonic pulsed phase-locked loop (PPLL) fascial displacement waveform analysis for noninvasive measurement of intramuscular pressure (IMP). Design Human subject experiment. Setting University Level 1 trauma center. Participants Nine male and 1 female volunteers (age 20 to 59),3 male acute compartment syndrome (ACS) patients (age 31 to 38). Intervention Thigh tourniquet was inflated in a stepwise fashion from 40 to 100 mm Hg to increase IMP transiently in volunteers. Main Outcome Measurements Invasive IMP by slit catheter and PPLL fascial displacement waveform in volunteers with model ACS and patients with ACS. Results In the model compartment tamponade group, thigh cuff occlusion increased IMP in the anterior compartment from a mean of 12.1 mm Hg (SE=1.5) to a mean of 27.4 mm Hg (SE=2.4, N=8, P<0.0001). By fast Fourier transform, the ratio of the amplitude of the fundamental frequency to the amplitude of the second harmonic frequency of the fascial displacement waveform as measured by PPLL increased from a resting mean of 1.12 (SE=0.07) to a mean of 1.85 (SE=0.18) under the same protocol (N=6, P=0.001). Combined data with compartment syndrome patients revealed linear correlation between IMP and PPLL with an R2 value of 0.8887. Conclusions Subarterial thigh cuff pressure causes a significant and transient increase in IMP, serving as a model for anterior compartment tamponade. PPLL is able to detect fascial displacement waveforms corresponding to arterial pulsation and furthermore distinguishes between normal and elevated IMP. There is a linear correlation between PPLL measurements and invasive IMP. The PPLL shows potential utility as a device for noninvasive measurement of IMP for detecting compartment syndromes.

Comparison of Mechanical Stability in Double-Row Rotator Cuff Repairs Between a Knotless Transtendon Construct Versus the Addition of Medial Knots

PURPOSE Our purpose was to investigate the importance of medial-row knot tying to mechanical stability in a double-row rotator cuff repair by comparing a knotless construct with transtendon anchor passage versus a similar construct implementing medial knots. METHODS A standard defect was created in the infraspinatus tendons of 14 bovine humeri. All defects were repaired with 2 medial and 2 lateral anchors (SutureCross System; KFx Medical, Carlsbad, CA). The medial anchors were either placed by transtendon passage in a knotless construct or placed directly into bone with needle passage of suture to create bursal-sided knots medially. Constructs were subjected to a cyclic loading protocol and then loaded to failure. RESULTS The medially knotted constructs had a statistically higher stiffness at both the initial and final cycles (P < .001 and P < .001, respectively) and a lower displacement during cyclic loading (P < .02). There were strong trends toward decreased gauge displacement (P = .12) and decreased cycles to 3 mm of displacement (P = .07) in the medially knotted group. Maximal yield strength was greater in the medially knotted group (350 +/- 270 N v 650 +/- 530 N), although this was not found to be statistically significant (P = .5). CONCLUSIONS Our data suggest that creation of medial knots increases construct stiffness and stability in arthroscopic double-row cuff repair. This is likely because of increased load transfer to the lateral anchor and suture-tendon interface in the knotless construct. CLINICAL RELEVANCE Medial knots create increased mechanical stability that theoretically may improve rotator cuff healing. This mechanical advantage must be weighed against surgical efficiency, with consideration given to factors such as tissue quality.

Augmentation of Tendon Healing With Butyric Acid–Impregnated Sutures Biomechanical Evaluation in a Rabbit Model

Background: Butyric acid (BA) has been shown to be angiogenic and to enhance transcriptional activity in tissue. These properties of BA have the potential to augment biological healing of a repaired tendon. Purpose: To evaluate this possibility both biomechanically and histologically in an animal tendon repair model. Study Design: Controlled laboratory study. Methods: A rabbit Achilles tendon healing model was used to evaluate the biomechanical strength and histological properties at 6 and 12 weeks after repair. Unilateral tendon defects were created in the middle bundle of the Achilles tendon of each rabbit, which were repaired equivalently with either Ultrabraid BA-impregnated sutures or control Ultrabraid sutures. Results: After 6 weeks, BA-impregnated suture repairs had a significantly increased (P < .0001) Young’s modulus and ultimate tensile strength relative to the control suture repairs. At 12 weeks, no statistical difference was observed between these measures. The histological data at 6 weeks demonstrated significantly increased (P < .005) vessel density within 0.25 mm of the repair suture in the BA-impregnated group. There was also an associated 42% increase in the local number of myofibroblasts in the BA samples relative to the controls at this time. By 12 weeks, these differences were not observed. Conclusion: Tendons repaired with BA-impregnated sutures demonstrated improved biomechanical properties at 6 weeks relative to control sutures, suggesting a neoangiogenic mechanism of enhanced healing through an increased myofibroblast presence. Clinical Relevance: These findings demonstrate that a relatively simple alteration of suture material may augment early tendon healing to create a stronger repair construct during this time.

Transient global amnesia: a complication of incremental exercise testing.

Incremental exercise testing is routinely used for diagnosis, rehabilitation, health screening, and research. We report the case of a 71-yr-old patient with chronic obstructive pulmonary disease (COPD) who suffered an episode of transient global amnesia (TGA) several minutes after successfully completing an incremental exercise test on a cycle ergometer. TGA, which is known to be precipitated by physical or emotional stress in about one-third of cases, is a transient neurological disorder in which memory impairment is the prominent deficit. TGA has a benign course and requires no treatment although 24-h observation is recommended. Recognition of TGA as a potential complication of incremental graded exercise testing is important to both aid diagnosis of the amnesia and to spare a patient unnecessary evaluation.

The Effect of Kneeling During Spine Surgery on Leg Intramuscular Pressure

BACKGROUND Acute compartment syndrome has been an underreported complication during spine surgery with the patient positioned on the so-called 90/90 kneeling frame (with 90 degrees of both hip and knee flexion), presumably because of elevated intramuscular pressures in the dependent leg compartments. The purpose of the present study was to characterize and quantify certain parameters that affect the risk for acute compartment syndrome experimentally and to make objective comparisons with other spine surgery positions. METHODS Eight healthy volunteers were positioned in three spine surgery positions: the 90/90 kneeling position, the so-called 45/45 suspended position (with the hips and knees both flexed to 45 degrees with the legs suspended on a sling), and the prone position. Intramuscular pressures were measured in all four left leg compartments with slit catheters. Local blood pressure and applied load beneath the leg were also measured. RESULTS The 90/90 kneeling position was associated with significantly increased intramuscular pressure in the anterior compartment (30.8 +/- 5.7 mm Hg) in comparison with the prone position (13.5 +/- 1.7 mm Hg) and the 45/45 suspended position (13.8 +/- 1.7 mm Hg). In the 90/90 kneeling position, these values correlated with subject weight (r = 0.72, p = 0.045) and the applied body weight load measured beneath the leg (r = 0.74, p = 0.037). The mean differences between intramuscular pressure and ankle blood pressure were more pronounced as the position of the ankle dropped below the level of the heart in the 45/45 suspended and the 90/90 kneeling positions. CONCLUSIONS The 90/90 kneeling position results in elevated intramuscular pressure in the anterior compartment of the leg. This elevated pressure correlates also with subject weight. The 90/90 kneeling position may predispose patients to the development of an acute compartment syndrome during prolonged spine surgery, with heavier patients being at increased risk. In certain instances, the surgeon may consider using the 45/45 suspended position to minimize this risk.

Paraspinal Muscle Vasculature Contributes to Posterolateral Spinal Fusion

Study Design. Study of posterolateral fusions in a rabbit model. Objectives. To characterize the contribution of paraspinal musculature to the healing of posterolateral spinal fusions in a rabbit model. Summary of Background Data. Previous studies have demonstrated that successful spinal arthrodesis requires vascular ingrowth from adjacent decorticated bone. In other areas of the body, such as the tibia, vascular ingrowth from the surrounding musculature has also been shown to be important. The role of the surrounding paraspinal musculature in spinal fusions has yet to be assessed. Methods. Twenty-five New Zealand white rabbits underwent posterolateral spinal fusion. One side of the animals was treated with autograft alone and served as the control group. On the contralateral side, the autograft was contained within porous or nonporous barrier sheets. Following euthanization, high-resolution radiographs, CT scans, and histologic analyses were performed to assess fusion and characterize vascular ingrowth. Results. Using histologic evaluation, the fusion rate in the porous group was 90%, in the nonporous group 40%, and in the control group 55%. Vascular ingrowth was evident from the muscle through the porous sheet into the fusion mass. Conclusions. These results support our hypothesis that the paraspinal musculature provides important vascular ingrowth into the fusion site. Use of a porous barrier sheet appears to improve fusion by preventing muscle interposition while allowing vascular ingrowth from surrounding muscle.