- Email: [email protected]
Optimizing intramedullary entry location on the proximal humerus based on variations of neck-shaft angle
J Shoulder Elbow Surg (2015) -, 1-5
www.elsevier.com/locate/ymse
Optimizing intramedullary entry location on the proximal humerus based on variations of neck-shaft angle Jinyoung Jeong, MD, PhD*, Hyun-Woo Jung, MD Department of Orthopaedic Surgery, St. Vincent’s Hospital, College of Medicine, The Catholic University of Korea, Suwon, South Korea Background: The purpose of this study was to define the relationship between the humeral neck-shaft angle (NSA) and variations in the ideal entry portal aligned with the long axis of the intramedullary canal of the proximal humerus. Methods: Three-dimensional images of 36 cadaveric humeri with various NSAs were reconstructed by a computerized surgical simulation program. The anteroposterior, mediolateral, and linear distances between a line from the center of the proximal medullary canal to the bicipital groove were measured. Differences among humeri with various NSAs were analyzed. Results: The intramedullary axis line was located a mean of 9 2 mm posteriorly and 11 3 mm medially from the bicipital groove. The axis line was 9 2 mm posterior and 11 2 mm medial with a standard NSA. The axis line in humeri with a varus NSA was 8 2 mm posteriorly and 9 2 mm medially, whereas the axis line was 10 3 mm posteriorly and 14 3 mm medially with a valgus NSA. The differences in the mediolateral distances between the groups were significant (P < .00009). Conclusion: Care should be taken in choosing the entry portal position in humeri with various NSAs as the entry portal position differs according to the NSA. It is recommended that the location of the entry portal be moved toward the center of the humeral head to align with the centerline of the intramedullary canal in humeri with a valgus NSA in particular. Level of evidence: Basic Science Study, Anatomy, Surgical Technique. Ó 2015 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Proximal humerus; neck-shaft angle; portal of entry; intramedullary prosthesis; 3-dimensional; cadaveric study
This study was funded by 2011 grants (SVHR-2010-15) from the Clinical Research Institute of St. Vincent’s Hospital, The Catholic University of Korea. Institutional Review Board approval was provided by St. Vincent’s Hospital, The Catholic University of Korea: No. VC11SISI0162. *Reprint requests: Jinyoung Jeong, MD, PhD, Department of Orthopaedic Surgery, St. Vincent’s Hospital, College of Medicine, The Catholic University of Korea, 93-6 Ji-dong, Paldal-gu, Suwon, Gyeonggi-do, Korea 442-723. E-mail address: [email protected] (J. Jeong).
Properly locating the entry portal for proximal arthroplasty or intramedullary nailing of the humerus is important as an improper insertion point leads to unsatisfactory results.3,7,10,13,15,17,18,20,21 As anatomically significant variations in the proximal humerus have been reported,5,8,9,11,12,22-24 it is important to define the relationship between the ideal entry point and variations in the neck-shaft angle (NSA) of the proximal humerus. Mean
1058-2746/$ - see front matter Ó 2015 Journal of Shoulder and Elbow Surgery Board of Trustees. http://dx.doi.org/10.1016/j.jse.2015.01.016
2
J. Jeong, H.-W. Jung
NSA was 135 in a study that used a 3-dimensional (3D) reconstruction program. The NSAs in 78% of the humeri were within 5 of the mean value of 135 , yet 22% of the humeri were either above 140 or below 130 .11 Therefore, it is important to estimate the entry point for the intramedullary prosthesis during fracture or prosthetic replacement surgeries, depending on the proximal humerus NSA, to maintain normal anatomic reconstruction of the proximal humerus. Failure of anatomic reconstruction of the humerus due to an incorrect entry portal may result in malpositioning of the stem or humeral rod. A malpositioned prosthesis can result in altered joint kinematics, whereas a malpositioned intramedullary rod can result in nonunion, malunion, or refracture.6,25 The ideal position for the entry portal can be determined by an extension line that represents the center of the proximal diaphysis of the medullary canal to the humeral head if the intramedullary rod is straight,3,17 and depending on the shape of the proximal humerus or humeral head, this entry point should be different. Therefore, our hypothesis was that depending on the variations of NSA of the proximal humerus, the entry point for the intramedullary rod or prosthesis should be different. In this study, the location of the ideal entry portal at the anatomic neck or at the top of the humeral head was correlated with NSA. No 3D studies have been conducted on the exact entry portal for an intramedullary device during anatomic reconstruction of proximal humeri with various NSAs. Thus, we determined the ideal entry portal position on the humerus on the basis of humeri with wide variations in NSA using a 3D reconstruction program.
The 36 cadaveric humeri were scanned with a 64-detector computed tomography scanner (Siemens Sensation 64; Siemens Medical Solutions, Malvern, PA, USA) using 1-mm axial increments and a B60 reconstruction kernel. The 3D reconstruction was created from 2-dimensional Digital Imaging and Communications in Medicine images (Cleveland Clinic, Cleveland, OH, USA).11 The centerline of the medullary canal of the humeral shaft was defined by an automated function in the software. The straight portion of the proximal third of the humeral shaft distal to the head was interactively selected by the surgeon, and the algorithm determined the best-fit line to a series of marrow space centroids in the intramedullary space detected in the selected region. The entry portal position was assigned as an extension of the centerline of the medullary canal onto the humeral head (C in Fig. 1). The position of the centerline of the medullary canal on the transverse plane at the beginning of the bicipital groove was measured in anteroposterior (AP), mediolateral (ML), and linear (DL) directions from the base point of the bicipital groove (B in Fig. 1). The line for the AP distance was parallel to the anatomic neck plane, and the line for the ML distance was perpendicular to the AP line. The DL was the shortest line connecting C and B (Fig. 1).
Materials and methods
The centerline of the intramedullary canal for all 36 humeri was located a mean of 9 2 mm posterior (AP), 11 3 mm medial (ML), and 14 3 mm linear (DL) from the bicipital groove. The measurements for the 3 groups are summarized on Table I. The differences in ML and DL between the groups were significant (P ¼ .00009, P ¼ .00007). In pairwise multiple comparisons of ML, including varus vs. standard, varus vs. valgus, and standard vs. valgus NSAs, the DL of varus vs. valgus and the DL of standard vs. valgus were significantly different. However, no differences were observed in the AP distance between the groups (Table I).
This is a basic science study using cadaveric humerus. The study subjects were 36 cadaveric humeri with various NSAs preserved in the Cleveland Museum of Natural History (Hamann-Todd Osteological Collection, Cleveland, OH, USA), which were the same specimens used in our previous study.11 The humeri selected were free from traumatic or degenerative changes. Within the 36 humeri, mean age was 44 years (range, 30-78 years). Twenty of the 36 specimens were male, and there were the same number of right and left humeri. NSA was defined as the intersection of the axis of the proximal part on the humeral shaft and a line drawn perpendicular to the anatomic neck. This could be measured with the computer program by placing 3 markers on the border of the anatomic neck and obtaining the shaft axis of the proximal humerus, which was interactively selected by the surgeon. The algorithm of the software determined the axis and angle, and the reliability and the accuracy of these measurements were validated in the previous study. The average NSA was 133.4 (range, 121 144 ). The humeri were categorized into 3 groups of varus (NSA, 120 -129 ; n ¼ 13), standard (130 -139 ; n ¼ 16), and valgus (140 -149 ; n ¼ 7). The groups were created on the basis of the clinical assumption that a deviation of 5 on either side of the average NSA neither was clinically relevant nor could be accurately controlled by standard surgical tools and methods.
Statistical analysis Means and standard deviations of the AP, ML, and DL were calculated on the basis of humeral NSA. These variables were considered continuous, and the analysis was performed by 1-way analysis of variance or the Kruskal-Wallis H test. The groups were compared with the t test using SigmaPlot 10 (Systat Software, San Jose, CA, USA). The accuracy and reproducibility of measuring the NSA and the measurement definitions were reported previously.11
Results
Discussion Normal variations in the proximal humerus have been reported in many studies.7-14,16 Deviations from normal proximal humerus anatomy during reconstructive surgery can cause negative biomechanical effects on the shoulder.6,7,16,25 In addition, insertion of an intramedullary prosthesis through an incorrect entry portal may cause a number of complications, such as fracture, nonunion,
Entry portal for intramedullary prosthetics
3
Figure 1 (A) The ideal position of the entry portal can be determined at the point of a projection line of the centroid of the medullary canal to the humeral head. (B) Distances between the projection point of centerline of the proximal medullary canal and the base of the bicipital groove. AP, anterior to posterior distance; ML, medial to lateral distance; DL, linear distance; B, base of bicipital groove; C, point of centerline of the canal; AN, anatomic neck plane.
Table I The distances between the centerline of the proximal medullary canal and the bicipital groove were measured in anteroposterior, mediolateral, and linear directions Parameters
Varus NSA (n ¼ 13)
Standard NSA (n ¼ 16)
Valgus NSA (n ¼ 7)
All (N ¼ 36)
Average NSA (degrees) AP (mm) ML (mm) DL (mm)
127 2
135 3
142 1
133.4 6.1
82 92 12 2
92 11 2 14 2
10 3 14 3 18 2
92 11 3 14 3
P value
Varus vs. standard
Varus vs. valgus
Standard vs. valgus
.044 .00009 .000007
.33 .0086 .0082
.016 .00016 .000016
.09 .0095 .0014
AP, anteroposterior; ML, mediolateral; DL, linear distance; NSA, neck-shaft angle.
malunion, and overstuffing or understuffing.1,14 Proper selection of the entry site for the intramedullary nail of the humerus could reduce the risk of these complications and better approximate neutral alignment of the humeral stem with the humeral shaft.4 Blum et al2 reported the correct entry portal for an intramedullary prosthesis as the margin of the humeral head cartilage medial to the greater tuberosity, whereas Rajasekhar et al19 described an entry portal located immediately medial to the greater tuberosity and approximately 1.5 cm posterior to the bicipital groove. As shown in many studies, each researcher describes a different location for the correct entry portal. In general, the standard entry portal is medial to the greater tuberosity and posterior to the bicipital groove. However, these studies did not correlate the entry portal with variations in humeral NSA. This may in part explain the variations in the reported entry portal locations among these studies. Noda et al15
presented a cadaveric study regarding the location of the entry point of the intramedullary nail for the proximal humeral fracture. They found that even with a correct entry point, cortical apposition may be lost after the insertion of the nail. However, they used the same entry point for all the specimens, although there were no data regarding anatomic variations such as NSA, retroversion, and head size. We think this can be one of the possible reasons for the deviation of the fracture reduction after introduction of the intramedullary nail. It seems intuitive that the position of the entry portal would vary according to the shape of the proximal humerus, particularly the NSA or the humerus type. Moreover, about 20% of humeri have a high valgus or varus NSA11; that is, there is a 20% chance that a surgeon will encounter a humerus with variations. The entry portal position for a humerus with a standard NSA does not differ from the currently known location,1,2,4,14,19 as measured
4
J. Jeong, H.-W. Jung
Figure 2 The position of the entry portal for the humeri with varus and valgus neck-shaft angle tends to move laterally or medially from that in standard neck-shaft angle. (A) Humerus with varus neck-shaft angle. (B) Humerus with valgus neck-shaft angle.
9 mm posterior and 11 mm medial to the bicipital groove in this study. However, this location point tended to move more posteriorly and medially in the valgus group, whereas it was more anterior and lateral from the standard group location in the varus group (Fig. 2). The differences in the distances between the valgus and standard groups were greater than those between the varus and standard groups, suggesting that care should be taken particularly for humeri with a valgus NSA. Insertion of an intramedullary prosthesis through the conventional entry portal in humeri with a valgus NSA could cause angulation of the stem or damage to the humeral shaft cortex. Thus, the entry portal should be moved medial and posterior to the usual point to locate the intramedullary stem in the center of the canal. It is impossible to determine accurate placement of the entry portal on preoperative plain radiographs or computed tomography scans. However, we accurately located the correct position on a 3D humeral head using a 3D reconstruction program that automatically calculated and determined the humeral shaft centroid, as the ideal entry point should be at the point of a projection line from the medullary canal centroid to the humeral head if the implant or intramedullary rod is straight. This is one of the strengths of this study. Nevertheless, there were several limitations in this study. First, only 36 humeri were analyzed, which does not represent all clinical cases. Factors such as retroversion and head size of the humerus as well as the pathologic condition of the humeri, including arthritis, trauma, and deformation, were not considered and should be evaluated in a future study. Second, we did not clinically evaluate whether a difference of a few millimeters would make a difference in the cancellous bone,
which is soft enough in most patients that a reamer selflocalizes with the endosteal cortical surface of the diaphysis based on alignment of the intramedullary reamer. Last, this study was conducted under the premise that the implant was straight, so the shape and angle of the proximal portion of the prosthesis or nail should be considered in a clinical situation.
Conclusions Selection of the entry location for a stemmed humeral prosthesis or intramedullary rod is important and should be modified according to variations in the humerus NSA. In particular, the entry portal position should be moved toward the center of the humeral head for better anatomic reconstruction results in humeri with a valgus NSA.
Acknowledgment We would like to acknowledge Dr. Joseph P. Iannotti, who helped with giving comments and suggestions on this study.
Disclaimer The authors, their immediate families, and any research foundation with which they are affiliated have not
Entry portal for intramedullary prosthetics received any financial payments or other benefits from any commercial entity related to the subject of this article.
References 1. Agel J, Jones CB, Sanzone AZ, Camuso M, Henley MB. Treatment of proximal humeral fractures with Polarus nail fixation. J Shoulder Elbow Surg 2004;13:191-5. http://dx.doi.org/10.1016/j.jse.2003.12.005 2. Blum J, Janzing H, Gahr R, Langendorff HS, Rommens PM. Clinical performance of a new medullary humeral nail: antegrade versus retrograde insertion. J Orthop Trauma 2001;15:342-9. 3. Boileau P, Walch G. The three-dimensional geometry of the proximal humerus. Implications for surgical technique and prosthetic design. J Bone Joint Surg Br 1997;79:857-65. 4. Cox MA, Dolan M, Synnott K, McElwain JP. Closed interlocking nailing of humeral shaft fractures with the Russell-Taylor nail. J Orthop Trauma 2000;14:349-53. 5. DeLude JA, Bicknell RT, MacKenzie GA, Ferreira LM, Dunning CE, King GJW, et al. An anthropometric study of the bilateral anatomy of the humerus. J Shoulder Elbow Surg 2007;16:477-83. http://dx.doi. org/10.1016/j.jse.2006.09.016 6. Fischer LP, Carret JP, Gonon GP, Dimnet J. Cinematic study of the movements of the scapulo-humeral (articulatio humeri) joint. Rev Chir Orthop Reparatrice Appar Mot 1977;63(Suppl 2):108-15. 7. Harryman DT, Sidles JA, Harris SL, Lippitt SB, Matsen FA. The effect of articular conformity and the size of the humeral head component on laxity and motion after glenohumeral arthroplasty. A study in cadavera. J Bone Joint Surg Am 1995;77:555-63. 8. Hertel R, Knothe U, Ballmer FT. Geometry of the proximal humerus and implications for prosthetic design. J Shoulder Elbow Surg 2002; 11:331-8. http://dx.doi.org/10.1067/mse.2002.124429 9. Iannotti JP, Gabriel JP, Schneck SL, Evans BG, Misra S. The normal glenohumeral relationships. An anatomical study of one hundred and forty shoulders. J Bone Joint Surg Am 1992;74:491-500. 10. Iannotti JP, Williams GR. Total shoulder arthroplasty. Factors influencing prosthetic design. Orthop Clin North Am 1998;29:377-91. 11. Jeong J, Bryan J, Iannotti JP. Effect of a variable prosthetic neck-shaft angle and the surgical technique on replication of normal humeral anatomy. J Bone Joint Surg Am 2009;91:1932-41. http://dx.doi.org/10. 2106/JBJS.H.00729
5 12. Jobe CM, Iannotti JP. Limits imposed on glenohumeral motion by joint geometry. J Shoulder Elbow Surg 1995;4:281-5. 13. Krishnan SG, Bennion PW, Reineck JR, Burkhead WZ. Hemiarthroplasty for proximal humeral fracture: restoration of the Gothic arch. Orthop Clin North Am 2008;39:441-50. http://dx.doi.org/10. 1016/j.ocl.2008.05.004 14. Mittlmeier TW, Stedtfeld HW, Ewert A, Beck M, Frosch B, Gradl G. Stabilization of proximal humeral fractures with an angular and sliding stable antegrade locking nail. J Bone Joint Surg Am 2003; 85(Suppl):136-46. 15. Noda M, Saegusa Y, Maeda T. Does the location of the entry point affect the reduction of proximal humeral fractures? A cadaveric study. Injury 2011;42:S35-8. http://dx.doi.org/10.1016/S0020-1383(11) 70010-9 16. Nyffeler RW, Sheikh R, Jacob HA, Gerber C. Influence of humeral prosthesis height on biomechanics of glenohumeral abduction. An in vitro study. J Bone Joint Surg Am 2004;86:575-80. 17. Park JY, Pandher DS, Chun JY, Lee ST. Antegrade humeral nailing through the rotator cuff interval: a new entry portal. J Orthop Trauma 2008;22:419-25. http://dx.doi.org/10.1097/BOT.0b013e318173f751 18. Pearl ML, Volk AG. Retroversion of the proximal humerus in relationship to prosthetic replacement arthroplasty. J Shoulder Elbow Surg 1995;4:286-9. 19. Rajasekhar C, Ray PS, Bhamra MS. Fixation of proximal humeral fractures with the Polarus nail. J Shoulder Elbow Surg 2001;10:7-10. 20. Rietveld AB, Daanen HA, Rozing PM, Obermann WR. The lever arm in glenohumeral abduction after hemiarthroplasty. J Bone Joint Surg Br 1988;70:561-5. 21. Roberts SN, Foley AP, Swallow HM, Wallace WA, Coughlan DP. The geometry of the humeral head and the design of prostheses. J Bone Joint Surg Br 1991;73:647-50. 22. Robertson DD, Yuan J, Bigliani LU, Flatow EL, Yamaguchi K. Threedimensional analysis of the proximal part of the humerus: relevance to arthroplasty. J Bone Joint Surg Am 2000;82:1594-602. 23. Roche C, Angibaud L, Flurin PH, Wright T, Fulkerson E, Zuckerman J. Anatomic validation of an ‘‘anatomic’’ shoulder system. Bull Hosp Jt Dis 2006;63:93-7. 24. Soslowsky LJ, Flatow EL, Bigliani LU, Mow VC. Articular geometry of the glenohumeral joint. Clin Orthop Relat Res 1992;285: 181-90. 25. Williams GR Jr, Wong KL, Pepe MD, Tan V, Silverberg D, Ramsey ML, et al. The effect of articular malposition after total shoulder arthroplasty on glenohumeral translations, range of motion, and subacromial impingement. J Shoulder Elbow Surg 2001;10:399-409.
www.elsevier.com/locate/ymse
Optimizing intramedullary entry location on the proximal humerus based on variations of neck-shaft angle Jinyoung Jeong, MD, PhD*, Hyun-Woo Jung, MD Department of Orthopaedic Surgery, St. Vincent’s Hospital, College of Medicine, The Catholic University of Korea, Suwon, South Korea Background: The purpose of this study was to define the relationship between the humeral neck-shaft angle (NSA) and variations in the ideal entry portal aligned with the long axis of the intramedullary canal of the proximal humerus. Methods: Three-dimensional images of 36 cadaveric humeri with various NSAs were reconstructed by a computerized surgical simulation program. The anteroposterior, mediolateral, and linear distances between a line from the center of the proximal medullary canal to the bicipital groove were measured. Differences among humeri with various NSAs were analyzed. Results: The intramedullary axis line was located a mean of 9 2 mm posteriorly and 11 3 mm medially from the bicipital groove. The axis line was 9 2 mm posterior and 11 2 mm medial with a standard NSA. The axis line in humeri with a varus NSA was 8 2 mm posteriorly and 9 2 mm medially, whereas the axis line was 10 3 mm posteriorly and 14 3 mm medially with a valgus NSA. The differences in the mediolateral distances between the groups were significant (P < .00009). Conclusion: Care should be taken in choosing the entry portal position in humeri with various NSAs as the entry portal position differs according to the NSA. It is recommended that the location of the entry portal be moved toward the center of the humeral head to align with the centerline of the intramedullary canal in humeri with a valgus NSA in particular. Level of evidence: Basic Science Study, Anatomy, Surgical Technique. Ó 2015 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Proximal humerus; neck-shaft angle; portal of entry; intramedullary prosthesis; 3-dimensional; cadaveric study
This study was funded by 2011 grants (SVHR-2010-15) from the Clinical Research Institute of St. Vincent’s Hospital, The Catholic University of Korea. Institutional Review Board approval was provided by St. Vincent’s Hospital, The Catholic University of Korea: No. VC11SISI0162. *Reprint requests: Jinyoung Jeong, MD, PhD, Department of Orthopaedic Surgery, St. Vincent’s Hospital, College of Medicine, The Catholic University of Korea, 93-6 Ji-dong, Paldal-gu, Suwon, Gyeonggi-do, Korea 442-723. E-mail address: [email protected] (J. Jeong).
Properly locating the entry portal for proximal arthroplasty or intramedullary nailing of the humerus is important as an improper insertion point leads to unsatisfactory results.3,7,10,13,15,17,18,20,21 As anatomically significant variations in the proximal humerus have been reported,5,8,9,11,12,22-24 it is important to define the relationship between the ideal entry point and variations in the neck-shaft angle (NSA) of the proximal humerus. Mean
1058-2746/$ - see front matter Ó 2015 Journal of Shoulder and Elbow Surgery Board of Trustees. http://dx.doi.org/10.1016/j.jse.2015.01.016
2
J. Jeong, H.-W. Jung
NSA was 135 in a study that used a 3-dimensional (3D) reconstruction program. The NSAs in 78% of the humeri were within 5 of the mean value of 135 , yet 22% of the humeri were either above 140 or below 130 .11 Therefore, it is important to estimate the entry point for the intramedullary prosthesis during fracture or prosthetic replacement surgeries, depending on the proximal humerus NSA, to maintain normal anatomic reconstruction of the proximal humerus. Failure of anatomic reconstruction of the humerus due to an incorrect entry portal may result in malpositioning of the stem or humeral rod. A malpositioned prosthesis can result in altered joint kinematics, whereas a malpositioned intramedullary rod can result in nonunion, malunion, or refracture.6,25 The ideal position for the entry portal can be determined by an extension line that represents the center of the proximal diaphysis of the medullary canal to the humeral head if the intramedullary rod is straight,3,17 and depending on the shape of the proximal humerus or humeral head, this entry point should be different. Therefore, our hypothesis was that depending on the variations of NSA of the proximal humerus, the entry point for the intramedullary rod or prosthesis should be different. In this study, the location of the ideal entry portal at the anatomic neck or at the top of the humeral head was correlated with NSA. No 3D studies have been conducted on the exact entry portal for an intramedullary device during anatomic reconstruction of proximal humeri with various NSAs. Thus, we determined the ideal entry portal position on the humerus on the basis of humeri with wide variations in NSA using a 3D reconstruction program.
The 36 cadaveric humeri were scanned with a 64-detector computed tomography scanner (Siemens Sensation 64; Siemens Medical Solutions, Malvern, PA, USA) using 1-mm axial increments and a B60 reconstruction kernel. The 3D reconstruction was created from 2-dimensional Digital Imaging and Communications in Medicine images (Cleveland Clinic, Cleveland, OH, USA).11 The centerline of the medullary canal of the humeral shaft was defined by an automated function in the software. The straight portion of the proximal third of the humeral shaft distal to the head was interactively selected by the surgeon, and the algorithm determined the best-fit line to a series of marrow space centroids in the intramedullary space detected in the selected region. The entry portal position was assigned as an extension of the centerline of the medullary canal onto the humeral head (C in Fig. 1). The position of the centerline of the medullary canal on the transverse plane at the beginning of the bicipital groove was measured in anteroposterior (AP), mediolateral (ML), and linear (DL) directions from the base point of the bicipital groove (B in Fig. 1). The line for the AP distance was parallel to the anatomic neck plane, and the line for the ML distance was perpendicular to the AP line. The DL was the shortest line connecting C and B (Fig. 1).
Materials and methods
The centerline of the intramedullary canal for all 36 humeri was located a mean of 9 2 mm posterior (AP), 11 3 mm medial (ML), and 14 3 mm linear (DL) from the bicipital groove. The measurements for the 3 groups are summarized on Table I. The differences in ML and DL between the groups were significant (P ¼ .00009, P ¼ .00007). In pairwise multiple comparisons of ML, including varus vs. standard, varus vs. valgus, and standard vs. valgus NSAs, the DL of varus vs. valgus and the DL of standard vs. valgus were significantly different. However, no differences were observed in the AP distance between the groups (Table I).
This is a basic science study using cadaveric humerus. The study subjects were 36 cadaveric humeri with various NSAs preserved in the Cleveland Museum of Natural History (Hamann-Todd Osteological Collection, Cleveland, OH, USA), which were the same specimens used in our previous study.11 The humeri selected were free from traumatic or degenerative changes. Within the 36 humeri, mean age was 44 years (range, 30-78 years). Twenty of the 36 specimens were male, and there were the same number of right and left humeri. NSA was defined as the intersection of the axis of the proximal part on the humeral shaft and a line drawn perpendicular to the anatomic neck. This could be measured with the computer program by placing 3 markers on the border of the anatomic neck and obtaining the shaft axis of the proximal humerus, which was interactively selected by the surgeon. The algorithm of the software determined the axis and angle, and the reliability and the accuracy of these measurements were validated in the previous study. The average NSA was 133.4 (range, 121 144 ). The humeri were categorized into 3 groups of varus (NSA, 120 -129 ; n ¼ 13), standard (130 -139 ; n ¼ 16), and valgus (140 -149 ; n ¼ 7). The groups were created on the basis of the clinical assumption that a deviation of 5 on either side of the average NSA neither was clinically relevant nor could be accurately controlled by standard surgical tools and methods.
Statistical analysis Means and standard deviations of the AP, ML, and DL were calculated on the basis of humeral NSA. These variables were considered continuous, and the analysis was performed by 1-way analysis of variance or the Kruskal-Wallis H test. The groups were compared with the t test using SigmaPlot 10 (Systat Software, San Jose, CA, USA). The accuracy and reproducibility of measuring the NSA and the measurement definitions were reported previously.11
Results
Discussion Normal variations in the proximal humerus have been reported in many studies.7-14,16 Deviations from normal proximal humerus anatomy during reconstructive surgery can cause negative biomechanical effects on the shoulder.6,7,16,25 In addition, insertion of an intramedullary prosthesis through an incorrect entry portal may cause a number of complications, such as fracture, nonunion,
Entry portal for intramedullary prosthetics
3
Figure 1 (A) The ideal position of the entry portal can be determined at the point of a projection line of the centroid of the medullary canal to the humeral head. (B) Distances between the projection point of centerline of the proximal medullary canal and the base of the bicipital groove. AP, anterior to posterior distance; ML, medial to lateral distance; DL, linear distance; B, base of bicipital groove; C, point of centerline of the canal; AN, anatomic neck plane.
Table I The distances between the centerline of the proximal medullary canal and the bicipital groove were measured in anteroposterior, mediolateral, and linear directions Parameters
Varus NSA (n ¼ 13)
Standard NSA (n ¼ 16)
Valgus NSA (n ¼ 7)
All (N ¼ 36)
Average NSA (degrees) AP (mm) ML (mm) DL (mm)
127 2
135 3
142 1
133.4 6.1
82 92 12 2
92 11 2 14 2
10 3 14 3 18 2
92 11 3 14 3
P value
Varus vs. standard
Varus vs. valgus
Standard vs. valgus
.044 .00009 .000007
.33 .0086 .0082
.016 .00016 .000016
.09 .0095 .0014
AP, anteroposterior; ML, mediolateral; DL, linear distance; NSA, neck-shaft angle.
malunion, and overstuffing or understuffing.1,14 Proper selection of the entry site for the intramedullary nail of the humerus could reduce the risk of these complications and better approximate neutral alignment of the humeral stem with the humeral shaft.4 Blum et al2 reported the correct entry portal for an intramedullary prosthesis as the margin of the humeral head cartilage medial to the greater tuberosity, whereas Rajasekhar et al19 described an entry portal located immediately medial to the greater tuberosity and approximately 1.5 cm posterior to the bicipital groove. As shown in many studies, each researcher describes a different location for the correct entry portal. In general, the standard entry portal is medial to the greater tuberosity and posterior to the bicipital groove. However, these studies did not correlate the entry portal with variations in humeral NSA. This may in part explain the variations in the reported entry portal locations among these studies. Noda et al15
presented a cadaveric study regarding the location of the entry point of the intramedullary nail for the proximal humeral fracture. They found that even with a correct entry point, cortical apposition may be lost after the insertion of the nail. However, they used the same entry point for all the specimens, although there were no data regarding anatomic variations such as NSA, retroversion, and head size. We think this can be one of the possible reasons for the deviation of the fracture reduction after introduction of the intramedullary nail. It seems intuitive that the position of the entry portal would vary according to the shape of the proximal humerus, particularly the NSA or the humerus type. Moreover, about 20% of humeri have a high valgus or varus NSA11; that is, there is a 20% chance that a surgeon will encounter a humerus with variations. The entry portal position for a humerus with a standard NSA does not differ from the currently known location,1,2,4,14,19 as measured
4
J. Jeong, H.-W. Jung
Figure 2 The position of the entry portal for the humeri with varus and valgus neck-shaft angle tends to move laterally or medially from that in standard neck-shaft angle. (A) Humerus with varus neck-shaft angle. (B) Humerus with valgus neck-shaft angle.
9 mm posterior and 11 mm medial to the bicipital groove in this study. However, this location point tended to move more posteriorly and medially in the valgus group, whereas it was more anterior and lateral from the standard group location in the varus group (Fig. 2). The differences in the distances between the valgus and standard groups were greater than those between the varus and standard groups, suggesting that care should be taken particularly for humeri with a valgus NSA. Insertion of an intramedullary prosthesis through the conventional entry portal in humeri with a valgus NSA could cause angulation of the stem or damage to the humeral shaft cortex. Thus, the entry portal should be moved medial and posterior to the usual point to locate the intramedullary stem in the center of the canal. It is impossible to determine accurate placement of the entry portal on preoperative plain radiographs or computed tomography scans. However, we accurately located the correct position on a 3D humeral head using a 3D reconstruction program that automatically calculated and determined the humeral shaft centroid, as the ideal entry point should be at the point of a projection line from the medullary canal centroid to the humeral head if the implant or intramedullary rod is straight. This is one of the strengths of this study. Nevertheless, there were several limitations in this study. First, only 36 humeri were analyzed, which does not represent all clinical cases. Factors such as retroversion and head size of the humerus as well as the pathologic condition of the humeri, including arthritis, trauma, and deformation, were not considered and should be evaluated in a future study. Second, we did not clinically evaluate whether a difference of a few millimeters would make a difference in the cancellous bone,
which is soft enough in most patients that a reamer selflocalizes with the endosteal cortical surface of the diaphysis based on alignment of the intramedullary reamer. Last, this study was conducted under the premise that the implant was straight, so the shape and angle of the proximal portion of the prosthesis or nail should be considered in a clinical situation.
Conclusions Selection of the entry location for a stemmed humeral prosthesis or intramedullary rod is important and should be modified according to variations in the humerus NSA. In particular, the entry portal position should be moved toward the center of the humeral head for better anatomic reconstruction results in humeri with a valgus NSA.
Acknowledgment We would like to acknowledge Dr. Joseph P. Iannotti, who helped with giving comments and suggestions on this study.
Disclaimer The authors, their immediate families, and any research foundation with which they are affiliated have not
Entry portal for intramedullary prosthetics received any financial payments or other benefits from any commercial entity related to the subject of this article.
References 1. Agel J, Jones CB, Sanzone AZ, Camuso M, Henley MB. Treatment of proximal humeral fractures with Polarus nail fixation. J Shoulder Elbow Surg 2004;13:191-5. http://dx.doi.org/10.1016/j.jse.2003.12.005 2. Blum J, Janzing H, Gahr R, Langendorff HS, Rommens PM. Clinical performance of a new medullary humeral nail: antegrade versus retrograde insertion. J Orthop Trauma 2001;15:342-9. 3. Boileau P, Walch G. The three-dimensional geometry of the proximal humerus. Implications for surgical technique and prosthetic design. J Bone Joint Surg Br 1997;79:857-65. 4. Cox MA, Dolan M, Synnott K, McElwain JP. Closed interlocking nailing of humeral shaft fractures with the Russell-Taylor nail. J Orthop Trauma 2000;14:349-53. 5. DeLude JA, Bicknell RT, MacKenzie GA, Ferreira LM, Dunning CE, King GJW, et al. An anthropometric study of the bilateral anatomy of the humerus. J Shoulder Elbow Surg 2007;16:477-83. http://dx.doi. org/10.1016/j.jse.2006.09.016 6. Fischer LP, Carret JP, Gonon GP, Dimnet J. Cinematic study of the movements of the scapulo-humeral (articulatio humeri) joint. Rev Chir Orthop Reparatrice Appar Mot 1977;63(Suppl 2):108-15. 7. Harryman DT, Sidles JA, Harris SL, Lippitt SB, Matsen FA. The effect of articular conformity and the size of the humeral head component on laxity and motion after glenohumeral arthroplasty. A study in cadavera. J Bone Joint Surg Am 1995;77:555-63. 8. Hertel R, Knothe U, Ballmer FT. Geometry of the proximal humerus and implications for prosthetic design. J Shoulder Elbow Surg 2002; 11:331-8. http://dx.doi.org/10.1067/mse.2002.124429 9. Iannotti JP, Gabriel JP, Schneck SL, Evans BG, Misra S. The normal glenohumeral relationships. An anatomical study of one hundred and forty shoulders. J Bone Joint Surg Am 1992;74:491-500. 10. Iannotti JP, Williams GR. Total shoulder arthroplasty. Factors influencing prosthetic design. Orthop Clin North Am 1998;29:377-91. 11. Jeong J, Bryan J, Iannotti JP. Effect of a variable prosthetic neck-shaft angle and the surgical technique on replication of normal humeral anatomy. J Bone Joint Surg Am 2009;91:1932-41. http://dx.doi.org/10. 2106/JBJS.H.00729
5 12. Jobe CM, Iannotti JP. Limits imposed on glenohumeral motion by joint geometry. J Shoulder Elbow Surg 1995;4:281-5. 13. Krishnan SG, Bennion PW, Reineck JR, Burkhead WZ. Hemiarthroplasty for proximal humeral fracture: restoration of the Gothic arch. Orthop Clin North Am 2008;39:441-50. http://dx.doi.org/10. 1016/j.ocl.2008.05.004 14. Mittlmeier TW, Stedtfeld HW, Ewert A, Beck M, Frosch B, Gradl G. Stabilization of proximal humeral fractures with an angular and sliding stable antegrade locking nail. J Bone Joint Surg Am 2003; 85(Suppl):136-46. 15. Noda M, Saegusa Y, Maeda T. Does the location of the entry point affect the reduction of proximal humeral fractures? A cadaveric study. Injury 2011;42:S35-8. http://dx.doi.org/10.1016/S0020-1383(11) 70010-9 16. Nyffeler RW, Sheikh R, Jacob HA, Gerber C. Influence of humeral prosthesis height on biomechanics of glenohumeral abduction. An in vitro study. J Bone Joint Surg Am 2004;86:575-80. 17. Park JY, Pandher DS, Chun JY, Lee ST. Antegrade humeral nailing through the rotator cuff interval: a new entry portal. J Orthop Trauma 2008;22:419-25. http://dx.doi.org/10.1097/BOT.0b013e318173f751 18. Pearl ML, Volk AG. Retroversion of the proximal humerus in relationship to prosthetic replacement arthroplasty. J Shoulder Elbow Surg 1995;4:286-9. 19. Rajasekhar C, Ray PS, Bhamra MS. Fixation of proximal humeral fractures with the Polarus nail. J Shoulder Elbow Surg 2001;10:7-10. 20. Rietveld AB, Daanen HA, Rozing PM, Obermann WR. The lever arm in glenohumeral abduction after hemiarthroplasty. J Bone Joint Surg Br 1988;70:561-5. 21. Roberts SN, Foley AP, Swallow HM, Wallace WA, Coughlan DP. The geometry of the humeral head and the design of prostheses. J Bone Joint Surg Br 1991;73:647-50. 22. Robertson DD, Yuan J, Bigliani LU, Flatow EL, Yamaguchi K. Threedimensional analysis of the proximal part of the humerus: relevance to arthroplasty. J Bone Joint Surg Am 2000;82:1594-602. 23. Roche C, Angibaud L, Flurin PH, Wright T, Fulkerson E, Zuckerman J. Anatomic validation of an ‘‘anatomic’’ shoulder system. Bull Hosp Jt Dis 2006;63:93-7. 24. Soslowsky LJ, Flatow EL, Bigliani LU, Mow VC. Articular geometry of the glenohumeral joint. Clin Orthop Relat Res 1992;285: 181-90. 25. Williams GR Jr, Wong KL, Pepe MD, Tan V, Silverberg D, Ramsey ML, et al. The effect of articular malposition after total shoulder arthroplasty on glenohumeral translations, range of motion, and subacromial impingement. J Shoulder Elbow Surg 2001;10:399-409.