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Retroversion of the proximal humerus in relationship to prosthetic replacement arthroplasty
J. Shoulder Elbow Surg. Volume 5, Number 2, Part 2
285
286
Abstracts
MORPHOMETRY OF THE PROXIMAL H U M E R A L ENDE Postacchini*, MD, S. Gumina**, MD, F. Randisi***, MD, L. Orsina****, PhD, *University of Modena; ** University "La Sapienza", Rome; ***Radiology, " B a m b i n o Gesfi", Rome, ***University "La Sapienza", Rome. ITALY. Little is known about the spatial geometry of the medullary canal of the humerus. This may explain why the humeral prostheses are presently made by means of the graphical techniques used for femural prostheses. Furthermore, no mathematical models have been used to study the shape of the humeral medullary canal. Material and methods. We have calculated, on standard radiographs, the values of the flare index and the curvature radius of 70 dried humeri. The curvature radius of the proximal medullary canal of the same humeri was determined applying a mathematical model to the data obtained by means of measures carried out on axial CT scans (by calculating the barycentres of the scans) and on three-dimensional reconstructions. The values obtained were compared with those calculated on radiographs. The results obtained with our technique were then compared with those obtained from raw data. Results. Our results show that no precise information on the spatial geometry of the humeral medullar canal can be obtained form radiographic studies. We also found that the proximal half of the humeral canal either sharply procurves, though to a mild extent, and then gradually becomes rectilinear, or gradually reaches the largest amount of curvature. On the frontal plane, the upper half of the medullar canal is cranially inward curved and distally outward curved, or vice versa. Conclusions. The results of this study give new information on the spatial geometry of the humeral medullary canal. Hence, while it seems impossible to improve beyond a certain limit the "fill" of the femural canal achieved by custom-made prostheses, the typical morphomeu'y of the humeral canal may lead to further improvements of the "fit" between the implant and the canal, compared with the currently available prosthe ses.
HUMERAL HEAD PROSTHETIC ARTHROPLASTY: SURGICALLY RELEVANT GEOMETRIC CONSIDERATIONS The relationship of the humeral head prosthesis to the humerus is a cntical determinant of the result in glenohumeral arthroplasty. With press-fit humeral prostheses, the position of the component is largely dictated by the reamed medullary canal. This study explores the geometric relationships of this surgically defined humeral reference, the ,,orthopaedic axis". This is the axis of a cylindric reamer or press-fit prosthetic stem inserted to the appropriate depth for the humeral prosthesis. In 10 cadaveric proximal humeri, we measured seven parameters in a mdiologic projection of the humerus on the plane transverse to the orthopaedic axis. We then determined the prosthetic geometry of a canal-fitting humeral component necessary to match the anatomical parameters. To examine the effect of changing component version, we determined the maximal angle of anteversion and retreversion achievable by rotation of the component about the orthopaedic axis without compromising the tuberosJties. In the maximal possible anteversion or retroversion, the combined head and neck length changed by only 2 mm. Thus the effect of component version of a press-fit prosthesis on glenohumeral soft-tissue tension is small. The study suggests that the surgeon controls relatively few important variables in a press-fit humeral arthroplasty. Kinematics of the arthroplasty are controlled primady by soft-tissue releases and the selection of the prosthetic head-neck length.
Authors ; Franz T. Ballmer, J o h n A. Sidles, Steven L i p p i t t and F r e d e r i c k A. M a t s e n U n i v e r s i t y of W a s h i n g t o n , D e p a r t m e n t of O r t h o p a e d i c s , Seattle, W A / U S A
B.
287
288
$89
RETROVERSION OF THE PROXIMAL HUMERUS IN RELATIONSHIP TO PROSTHETIC REPLACEMENT ARTHROPLASTY. M. L. Pearl, MD, & A. G. Volk, MD, Department of Orthopedics, Southern California Permanente Medical Group, Los Angeles, CA. Arthroplasty of the proximal humerus positions a prosthetic articular surface in relation to the humeral canal. Most descriptions of surgical technique recommend positioning the humeral component in 30~ to 45~ of retroversion relative to the flexed forearm. This study measured retroversion in relationship to the surgically reamed canal introducing a method of measurement pertinent to prosthetic reconstruction. The canals of 21 cadaverm humeri were reamed to the best surgical fit. The articular margins of the humeral heads were outlined with steel wire. The trochlear axes were transfLxed with Steinman pins. Under fluoroscopy, the humeri were rotated on a jig that allowed rotation around the reamer and measurement of retroversion relative to the plane of the articular surface. Retroversion of the proximal humerus is highly variable, ran$in$ in this study from 10~ ~ (mean 29.8~ The implications of this variability for prosthetic replacement arc compounded by the known variability in the carrying angle of the elbow. Anatomic reconstruction' of the rctroversion angle should be individualized. Palpation of the rotator cuff insertion is recommended prior to humeral head resection to avoid inadvertent cuff injury.
THE ANTERO-SUPERIOR EXPOSURE FOR TOTAL SHOULDER REPLACEMENT (T.S.R.). D.B. Mackenzie, South Africa. This paper reports the use of the antero-superior approach and not the results of T~ per me. Preference for this approach over the more commonly performed delto-pectoral ~route was prompted by dissatisfaction with the access of the glenoid face especially in the well-muscled patient. It is postulated that survlvorehip of T.S.R. will be enhanced by superior glenoid component fixation afforded by a more direct exposure permitting more precise bone ~reparation prior to PMMA cement delivery and prosthetic insertion. The antero-superior approach was first employed in T.S.R. in 1984. With increasing familiarity and satisfaction with the access it affords, it has been ~outinely employed in 162 cases in a total series of 227 unconstrained arthroplasties started in 1978. Since then, a single case of clinically obvious paralysis of the deltoid fibres, medial to the split, has been encountered. The technique; with special attention to patient positioning, other intra~operative precautions and eontraindications for its use will be discussed. C~reful clinical neurological evaluation, with particular r e f ~ to the function of the anterior deltoid fibres of the last 20 consecutive patients, revealed no obvious paresis. It is concluded that with meticulous attention to t e ~ and prevention of excessive deltoid splitting by careful blunt dissection and the use of a stay suture, iatrogenio injury to the nerve supply can be avoided. The anterosuperior approach provides a virtus~l "face-on" view of the glenoid, and is a safe and sahisfactery exposure for primary gleno-humerel arthroplasty.
285
286
Abstracts
MORPHOMETRY OF THE PROXIMAL H U M E R A L ENDE Postacchini*, MD, S. Gumina**, MD, F. Randisi***, MD, L. Orsina****, PhD, *University of Modena; ** University "La Sapienza", Rome; ***Radiology, " B a m b i n o Gesfi", Rome, ***University "La Sapienza", Rome. ITALY. Little is known about the spatial geometry of the medullary canal of the humerus. This may explain why the humeral prostheses are presently made by means of the graphical techniques used for femural prostheses. Furthermore, no mathematical models have been used to study the shape of the humeral medullary canal. Material and methods. We have calculated, on standard radiographs, the values of the flare index and the curvature radius of 70 dried humeri. The curvature radius of the proximal medullary canal of the same humeri was determined applying a mathematical model to the data obtained by means of measures carried out on axial CT scans (by calculating the barycentres of the scans) and on three-dimensional reconstructions. The values obtained were compared with those calculated on radiographs. The results obtained with our technique were then compared with those obtained from raw data. Results. Our results show that no precise information on the spatial geometry of the humeral medullar canal can be obtained form radiographic studies. We also found that the proximal half of the humeral canal either sharply procurves, though to a mild extent, and then gradually becomes rectilinear, or gradually reaches the largest amount of curvature. On the frontal plane, the upper half of the medullar canal is cranially inward curved and distally outward curved, or vice versa. Conclusions. The results of this study give new information on the spatial geometry of the humeral medullary canal. Hence, while it seems impossible to improve beyond a certain limit the "fill" of the femural canal achieved by custom-made prostheses, the typical morphomeu'y of the humeral canal may lead to further improvements of the "fit" between the implant and the canal, compared with the currently available prosthe ses.
HUMERAL HEAD PROSTHETIC ARTHROPLASTY: SURGICALLY RELEVANT GEOMETRIC CONSIDERATIONS The relationship of the humeral head prosthesis to the humerus is a cntical determinant of the result in glenohumeral arthroplasty. With press-fit humeral prostheses, the position of the component is largely dictated by the reamed medullary canal. This study explores the geometric relationships of this surgically defined humeral reference, the ,,orthopaedic axis". This is the axis of a cylindric reamer or press-fit prosthetic stem inserted to the appropriate depth for the humeral prosthesis. In 10 cadaveric proximal humeri, we measured seven parameters in a mdiologic projection of the humerus on the plane transverse to the orthopaedic axis. We then determined the prosthetic geometry of a canal-fitting humeral component necessary to match the anatomical parameters. To examine the effect of changing component version, we determined the maximal angle of anteversion and retreversion achievable by rotation of the component about the orthopaedic axis without compromising the tuberosJties. In the maximal possible anteversion or retroversion, the combined head and neck length changed by only 2 mm. Thus the effect of component version of a press-fit prosthesis on glenohumeral soft-tissue tension is small. The study suggests that the surgeon controls relatively few important variables in a press-fit humeral arthroplasty. Kinematics of the arthroplasty are controlled primady by soft-tissue releases and the selection of the prosthetic head-neck length.
Authors ; Franz T. Ballmer, J o h n A. Sidles, Steven L i p p i t t and F r e d e r i c k A. M a t s e n U n i v e r s i t y of W a s h i n g t o n , D e p a r t m e n t of O r t h o p a e d i c s , Seattle, W A / U S A
B.
287
288
$89
RETROVERSION OF THE PROXIMAL HUMERUS IN RELATIONSHIP TO PROSTHETIC REPLACEMENT ARTHROPLASTY. M. L. Pearl, MD, & A. G. Volk, MD, Department of Orthopedics, Southern California Permanente Medical Group, Los Angeles, CA. Arthroplasty of the proximal humerus positions a prosthetic articular surface in relation to the humeral canal. Most descriptions of surgical technique recommend positioning the humeral component in 30~ to 45~ of retroversion relative to the flexed forearm. This study measured retroversion in relationship to the surgically reamed canal introducing a method of measurement pertinent to prosthetic reconstruction. The canals of 21 cadaverm humeri were reamed to the best surgical fit. The articular margins of the humeral heads were outlined with steel wire. The trochlear axes were transfLxed with Steinman pins. Under fluoroscopy, the humeri were rotated on a jig that allowed rotation around the reamer and measurement of retroversion relative to the plane of the articular surface. Retroversion of the proximal humerus is highly variable, ran$in$ in this study from 10~ ~ (mean 29.8~ The implications of this variability for prosthetic replacement arc compounded by the known variability in the carrying angle of the elbow. Anatomic reconstruction' of the rctroversion angle should be individualized. Palpation of the rotator cuff insertion is recommended prior to humeral head resection to avoid inadvertent cuff injury.
THE ANTERO-SUPERIOR EXPOSURE FOR TOTAL SHOULDER REPLACEMENT (T.S.R.). D.B. Mackenzie, South Africa. This paper reports the use of the antero-superior approach and not the results of T~ per me. Preference for this approach over the more commonly performed delto-pectoral ~route was prompted by dissatisfaction with the access of the glenoid face especially in the well-muscled patient. It is postulated that survlvorehip of T.S.R. will be enhanced by superior glenoid component fixation afforded by a more direct exposure permitting more precise bone ~reparation prior to PMMA cement delivery and prosthetic insertion. The antero-superior approach was first employed in T.S.R. in 1984. With increasing familiarity and satisfaction with the access it affords, it has been ~outinely employed in 162 cases in a total series of 227 unconstrained arthroplasties started in 1978. Since then, a single case of clinically obvious paralysis of the deltoid fibres, medial to the split, has been encountered. The technique; with special attention to patient positioning, other intra~operative precautions and eontraindications for its use will be discussed. C~reful clinical neurological evaluation, with particular r e f ~ to the function of the anterior deltoid fibres of the last 20 consecutive patients, revealed no obvious paresis. It is concluded that with meticulous attention to t e ~ and prevention of excessive deltoid splitting by careful blunt dissection and the use of a stay suture, iatrogenio injury to the nerve supply can be avoided. The anterosuperior approach provides a virtus~l "face-on" view of the glenoid, and is a safe and sahisfactery exposure for primary gleno-humerel arthroplasty.