Marc A. Pizzimenti

Selective long-term reorganization of the corticospinal projection from the supplementary motor cortex following recovery from lateral motor cortex injury.

Brain injury affecting the frontal motor cortex or its descending axons often causes contralateral upper extremity paresis. Although recovery is variable, the underlying mechanisms supporting favorable motor recovery remain unclear. Because the medial wall of the cerebral hemisphere is often spared following brain injury and recent functional neuroimaging studies in patients indicate a potential role for this brain region in the recovery process, we investigated the long‐term effects of isolated lateral frontal motor cortical injury on the corticospinal projection (CSP) from intact, ipsilesional supplementary motor cortex (M2). After injury to the arm region of the primary motor (M1) and lateral premotor (LPMC) cortices, upper extremity recovery is accompanied by terminal axon plasticity in the contralateral CSP but not the ipsilateral CSP from M2. Furthermore, significant contralateral plasticity occurs only in lamina VII and dorsally within lamina IX. Thus, selective intraspinal sprouting transpires in regions containing interneurons, flexor‐related motor neurons, and motor neurons supplying intrinsic hand muscles, which all play important roles in mediating reaching and digit movements. After recovery, subsequent injury of M2 leads to reemergence of hand motor deficits. Considering the importance of the CSP in humans and the common occurrence of lateral frontal cortex injury, these findings suggest that spared supplementary motor cortex may serve as an important therapeutic target that should be considered when designing acute and long‐term postinjury patient intervention strategies aimed to enhance the motor recovery process following lateral cortical trauma. J. Comp. Neurol. 518:586–621, 2010.

Volumetric Effects of Motor Cortex Injury on Recovery of Dexterous Movements

Due to the heterogeneous nature of most brain injuries, the contributions of gray and white matter involvement to motor deficits and recovery potential remain obscure. We tested the hypothesis that duration of hand motor impairment and recovery of skilled arm and hand motor function depends on the volume of gray and white matter damage of the frontal lobe. Lesions of the primary motor cortex (M1), M1 + lateral premotor cortex (LPMC), M1 + LPMC + supplementary motor cortex (M2) or multifocal lesions affecting motor areas and medial prefrontal cortex were evaluated in rhesus monkeys. Fine hand motor function was quantitatively assessed pre-lesion and for 3-12 months post-lesion using two motor tests. White and gray matter lesion volumes were determined using histological and quantitative methods. Regression analyses showed that duration of fine hand motor impairment was strongly correlated (R(2)>0.8) with the volume of gray and white matter lesions, with white matter lesion volume being the primary predictor of impairment duration. Level of recovery of fine hand motor skill was also well correlated (R(2)>0.5) with gray and white matter lesion volume. In some monkeys post-lesion skill exceeded pre-lesion skill in one or both motor tasks demonstrating that continued post-injury task practice can improve motor performance after localized loss of frontal motor cortex. These findings will assist in interpreting acute motor deficits, predicting the time course and expected level of functional recovery, and designing therapeutic strategies in patients with localized frontal lobe injury or neurosurgical resection.

Risks to the blood supply of the talus with four methods of total ankle arthroplasty: a cadaveric injection study.

BACKGROUND Despite the use of contemporary total ankle arthroplasty implant designs, clinical outcomes of total ankle arthroplasty continue to lag behind those of other joint replacement procedures. Disruption of the extraosseous talar blood supply at the time of ankle replacement may be a factor contributing to talar component subsidence-a common mechanism of early failure following ankle replacement. We evaluated the risk of injury to specific extraosseous arteries supplying the talus associated with specific total ankle arthroplasty implants. METHODS Sixteen fresh-frozen through-knee cadaveric specimens were injected with latex and barium sulfate distal to the popliteal trifurcation to visualize the arteries. Four specimens each were prepared for implantation of four contemporary total ankle arthroplasty systems: Scandinavian Total Ankle Replacement (STAR), INBONE II, Salto Talaris, and Trabecular Metal Total Ankle (TMTA). Postoperative computed tomography scans and 6% sodium hypochlorite chemical debridement were used to examine, measure, and document the proximity of the total ankle arthroplasty instrumentation to the extraosseous talar blood supply. RESULTS All four implant types subjected the extraosseous talar blood supply to the risk of injury. The INBONE subtalar drill hole directly transected the artery of the tarsal canal in three of four specimens. The lateral approach for the TMTA transected the first perforator of the peroneal artery in two of four specimens. The STAR caused medial injury to the deltoid branches in all four specimens, whereas the other three systems did not directly affect this supply (p < 0.005). The Salto Talaris and STAR implants caused injury to the artery of the tarsal canal in one of four specimens. CONCLUSIONS All four total ankle arthroplasty systems tested posed a risk of injury to the extraosseous talar blood supply, but the risks of injury to specific arteries were higher for specific implants.

Terminal distribution of the corticospinal projection from the hand/arm region of the primary motor cortex to the cervical enlargement in rhesus monkey.

To further our understanding of the corticospinal projection (CSP) from the hand/arm representation of the primary motor cortex (M1), high‐resolution anterograde tracing methodology and stereology were used to investigate the terminal distribution of this connection at spinal levels C5 to T1. The highest number of labeled terminal boutons occurred contralaterally (98%) with few ipsilaterally (2%). Contralaterally, labeled boutons were located within laminae I–X, with the densest distribution found in lamina VII and, to a lesser extent, laminae IX and VI. Fewer terminals were found in other contralateral laminae. Within lamina VII, terminal boutons were most prominent in the dorsomedial, dorsolateral, and ventrolateral subsectors. Within lamina IX, the heaviest terminal labeling was distributed dorsally. Ipsilaterally, boutons were found in laminae V–X. The most pronounced distribution occurred in the dorsomedial and ventromedial sectors of lamina VII and fewer labeled boutons were located in other ipsilateral laminae. Segmentally, contralateral lamina VII labeling was highest at levels C5–C7. In contrast, lamina IX labeling was highest at C7–T1 and more widely dispersed among the quadrants at C8–T1. Our findings suggest dominant contralateral influence of the M1 hand/arm CSP, a contralateral innervation pattern in lamina VII supporting Kuypers (1982) conceptual framework of a “lateral motor system,” and a projection to lamina IX indicating significant influence on motoneurons innervating flexors acting on the shoulder and elbow rostrally (C5–C7), along with flexors, extensors, abductors and adductors acting on the digits, hand and wrist caudally (C8–T1). J. Comp. Neurol. 521:4205–4235, 2013.

FUNCTIONAL RECOVERY FOLLOWING MOTOR CORTEX LESIONS IN NON-HUMAN PRIMATES:EXPERIMENTAL IMPLICATIONS FOR HUMAN STROKE PATIENTS

This review discusses selected classical works and contemporary research on recovery of contralesional fine hand motor function following lesions to motor areas of the cerebral cortex in non-human primates. Findings from both the classical literature and contemporary studies show that lesions of cortical motor areas induce paresis initially, but are followed by remarkable recovery of fine hand/digit motor function that depends on lesion size and post-lesion training. Indeed, in recent work where considerable quantification of fine digit function associated with grasping and manipulating small objects has been observed, very favorable recovery is possible with minimal forced use of the contralesional limb. Studies of the mechanisms underlying recovery have shown that following small lesions of the digit areas of primary motor cortex (M1), there is expansion of the digit motor representations into areas of M1 that did not produce digit movements prior to the lesion. However, after larger lesions involving the elbow, wrist and digit areas of M1, no such expansion of the motor representation was observed, suggesting that recovery was due to other cortical or subcortical areas taking over control of hand/digit movements. Recently, we showed that one possible mechanism of recovery after lesion to the arm areas of M1 and lateral premotor cortex is enhancement of corticospinal projections from the medially located supplementary motor area (M2) to spinal cord laminae containing neurons which have lost substantial input from the lateral motor areas and play a critical role in reaching and digit movements. Because human stroke and brain injury patients show variable, and usually poorer, recovery of hand motor function than that of nonhuman primates after motor cortex damage, we conclude with a discussion of implications of this work for further experimentation to improve recovery of hand function in human stroke patients.

Fostering interprofessional teamwork in an academic medical center: Near-peer education for students during gross medical anatomy.

The purpose of this report is to describe student satisfaction with a near‐peer interprofessional education (IPE) session for physical therapy and medical students. Ten senior physical therapy students worked in peer‐groups to develop a musculoskeletal anatomy demonstration for first‐semester medical students. Together with their classmates, they demonstrated observation, palpation, and musculoskeletal assessment of the shoulder and scapular‐thoracic articulation to medical student dissection groups in the Gross Anatomy laboratory. The medical students were encouraged to consider the synergistic function of shoulder structures and the potential impact of a selected pathology: rotator cuff injury. The session provided the medical students with an opportunity to integrate their new anatomical knowledge into a framework for clinical musculoskeletal evaluation. The experience offered senior physical therapy students an opportunity to work in teams with their peers, internalize and adapt to constructive feedback, and seek common ground with members of another profession. Both student groups reported a high degree of satisfaction with the sessions and expressed a desire for further interaction. These positive perceptions by student stakeholders have prompted us to consider additional IPE exchanges for the anatomy course in the upcoming school year. Given the positive outcome of this descriptive study, we now plan to systematically test whether near‐peer IPE interactions can enhance the degree that students learn key anatomical concepts. Anat Sci Educ 8: 331–337.

Unilateral posterior parietal lobe lesions affect representation of visual space

This study assessed accuracy of visually perceived vertical and trunk median plane orientation in 41 subjects: 17 had unilateral brain lesions including the posterior parietal lobe (PPL), 8 had lesions outside PPL, and 16 were neurologically normal. Vertical perception errors clearly increased with size of unilateral lesions to PPL and posterior superior temporal gyrus (PSTG). Median plane perception errors increased only slightly with size of unilateral lesions to frontal lobe premotor areas and supramarginal gyrus. These results are compatible with the hypothesis that accurate visual vertical perception depends critically on intact PPL and PSTG in both cerebral hemispheres while accurate median plane perception likely involves a bihemispheric network that can compensate for lesions to one hemisphere.

Vascular Disruption of the Talus Comparison of Two Approaches for Triple Arthrodesis

Background: For triple arthrodesis, a single medial incision has been proposed to avoid lateral wound complications and has demonstrated satisfactory fusion rates. This study aimed to compare the disruption to the arterial supply of the talus between the single-medial-incision approach and the 2-incision approach. Methods: The 2 approaches for triple arthrodesis were compared by analyzing the disruption of arterial vasculature in 14 cadaveric specimens in randomized fashion. The arterial disruption was determined using CT angiography before and after surgery combined with analysis from dissection. The area of joint preparation from each technique was also analyzed and compared. Results: The single-medial-incision approach caused a high incidence of damage to the deltoid artery (6 of 7 specimens, 86%) and the artery of the tarsal canal (7 of 7 specimens, 100%). The 2-incision approach resulted in damage to the artery of the tarsal sinus in all specimens (7 of 7 specimens, 100%), but the medial vasculature was spared given the limited dissection required to access the talonavicular joint. Through the single-medial-incision approach the percentage of debridement of the calcaneocuboid joint (36%) was significantly lower than the debridement using the 2-incision approach (85%, P < .01). There was no significant difference in joint preparation of the talonavicular and subtalar joints between the 2 approaches with the number of specimens available. Conclusion: From this cadaveric study, we found that both approaches could result in substantial disruption of the main blood supply to the talus. The single-medial-incision approach consistently disrupted the majority of blood supply to the talar body, while the 2-incision approach caused various degrees of vascular disruption to the talar head and neck. Using the single-medial-incision approach, the calcaneocuboid joint did not show adequate removal of articular cartilage due to difficulty accessing the joint surfaces. Clinical Relevance: Vascular sparing to the talus should be considered when selecting an appropriate operative approach for triple arthrodesis. Although the clinical significance of this cadaveric study is limited, the 2-incision approach appeared to cause less vascular disruption to the talar body while allowing more complete joint preparation.

Volumetric effects of motor cortex injury on recovery of ipsilesional dexterous movements

Damage to the motor cortex of one hemisphere has classically been associated with contralateral upper limb paresis, but recent patient studies have identified deficits in both upper limbs. In non-human primates, we tested the hypothesis that the severity of ipsilesional upper limb motor impairment in the early post-injury phase depends on the volume of gray and white matter damage of the motor areas of the frontal lobe. We also postulated that substantial recovery would accompany minimal task practice and that ipsilesional limb recovery would be correlated with recovery of the contralesional limb. Gross (reaching) and fine hand motor functions were assessed for 3-12 months post-injury using two motor tests. Volumes of white and gray matter lesions were assessed using quantitative histology. Early changes in post-lesion motor performance were inversely correlated with white matter lesion volume indicating that larger lesions produced greater decreases in ipsilesional hand movement control. All monkeys showed improvements in ipsilesional hand motor skill during the post-lesion period, with reaching skill improvements being positively correlated with total lesion volume indicating that larger lesions were associated with greater ipsilesional motor skill recovery. We suggest that reduced trans-callosal inhibition from the lesioned hemisphere may play a role in the observed skill improvements. Our findings show that significant ipsilesional hand motor recovery is likely to accompany injury limited to frontal motor areas. In humans, more pronounced ipsilesional motor deficits that invariably develop after stroke may, in part, be a consequence of more extensive subcortical white and gray matter damage.

Frontal and frontoparietal injury differentially affect the ipsilateral corticospinal projection from the nonlesioned hemisphere in monkey (Macaca mulatta)

Upper extremity hemiplegia is a common consequence of unilateral cortical stroke. Understanding the role of the unaffected cerebral hemisphere in the motor recovery process has been encouraged, in part, by the presence of ipsilateral corticospinal projections (iCSP). We examined the neuroplastic response of the iCSP from the contralesional primary motor cortex (cM1) hand/arm area to spinal levels C5–T1 after spontaneous long‐term recovery from isolated frontal lobe injury and isolated frontoparietal injury. High‐resolution tract tracing, stereological, and behavioral methodologies were applied. Recovery from frontal motor injury resulted in enhanced numbers of terminal labeled boutons in the iCSP from cM1 compared with controls. Increases occurred in lamina VIII and the adjacent ventral sectors of lamina VII, which are involved in axial/proximal limb sensorimotor processing. Larger frontal lobe lesions were associated with greater numbers of terminal boutons than smaller frontal lobe lesions. In contrast, frontoparietal injury blocked this response; total bouton number was similar to controls, demonstrating that disruption of somatosensory input to one hemisphere has a suppressive effect on the iCSP from the nonlesioned hemisphere. However, compared with controls, elevated bouton numbers occurred in lamina VIII, at the expense of lamina VII bouton labeling. Lamina IX boutons were also elevated in two frontoparietal lesion cases with extensive cortical injury. Because laminae VIII and IX collectively harbor axial, proximal, and distal motoneurons, therapeutic intervention targeting the ipsilateral corticospinal linkage from cM1 may promote proximal, and possibly distal, upper‐limb motor recovery following frontal and frontoparietal injury. J. Comp. Neurol. 524:380–407, 2016.