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Elbow joint instability: A kinematic model
Elbow [olnt instability: A kinematic model Bo S. Olsen, MD, Morten G . Henriksen, MD, Jens O . Sejbjerq, MD, Peter Helrniq, MD, and Otto Sneppen, MD, DMSc, Aarhus, Denmark
The effect of simultoneous ulnar and radial col/ateral ligament division on the kinematics of the elbow joint is studied in a cadaveric model. Severance of the anterior part of the ulnar col/ateralligament and the annular ligament led to significant elbow joint instability in valgus and varus stress and in forced external and internal rotation. The mean maximum laxity in valgus stress and forced external rotation were 5.7' and 73.7'. The forearms of the elbow joint specimens were transfixed in maximum pronation. During valgus and varus stress the corresponding spontaneous ulnar rotation of the specimens was recorded. The reproducibility of the instability pattern suggests that this model is suitable for evaluating stabilizing procedures aimed at correction of elbow joint instability before these procedures are introduced into patient care. (J SHOULDER ELBOW SURG 7994;3: 743-50.)
The elbow is, except for the shoulder, the most frequently dislocated major [oint." 20 Complications such as reduction in joint movement, pain, and neurologic deficits have been reported. v ' A rare and usually severely disabling complication is chronic elbow joint instability, manifested either as instability to valgus stress or recurrent dislocations of the [oint.' Several operative procedures have been described by different authors for treatment of the chronically unstable elbow [oint." 9. 18. 19 The clinical results reported are good,s· 9. 18. 19 but the basic kinematic influence on the joint and late results of these procedures have not been reported. Elbow joint stability depends on the articular geometry and the soft tissues, including the muscles and the collateral liqornents." Previous studies have shown that the prime ligamentous stabilizer on the ulnar aspect of the elbow joint is the anterior part of the ulnar collateral ligament, (ACL)l1· 12.20.23 whereas the prime stabi-
From the Biomechonics Laboratory, Univers ity of Aarhus. Supported by a grant from The Orthopaedic Scientif ic Foundation, Aarhus. Reprint requests : Ba S. Olsen, MD, Biomechanic Laborato ry, Shoulder and Elbow Cl inic, University of Aarhus, Randersvej 1, DK-8200 Aarhus N , Denmark. Copyright © 1994 by Journal of Should er and Elbow Surgery Board of Trustees. 1058-2746/94/$3.00 + 0 32/1154380
lizer on the radial aspect of the joint is the an nular ligament (LA).l1 · 12.21 The ulnar part of the radial collateral ligament prevents posterolateral rotatory stability of the elbow joint, as described by O'Driscoll et a1. 15 • 16 Josefson" 4 reported in a clinical study that posterior elbow joint dislocation was associated with both medial and lateral ligamentous injury. Sajbierq et ol.," in an experimental study of elbow dislocation, described the simultaneous rupture of the ACL and the LA. Furthermore they claimed that posterolateral dislocation of the elbow could be produced only when a combined valgus and external rotatory torque was applied to the forearm. The object of the present study was to measure the laxity of the elbow joint specimens before and after severance of the prime medial and lateral ligamentous stabil izers , and when doing this to develop a reproducible kinematic elbow joint model, encompassing a well -described range of motion in which significant and reproducible ligamentous joint laxity could be induced. Such a model would allow evaluation of the stabilizing effects of reconstructive procedures aimed at correction of elbow joint instability.
MATERIAL AND METHODS Ten macroscopically normal, male, rightsided, osteoligamentous elbow preparations
143
144 Olsen et 01.
1. Shoulder Elbow Surg. May/June 1994
1
1
Voltmeter '. Potentiometers
Rotational torque
X-V-Recorder Valgus/varus moment ••
~train
Gauges
...
Potentio~eie; • • : •
Figure 1 Experimental apparatus used to test stability of the elbow joint.
were studied. The median age at death of the cadaveric donors was 68 years (range 58 to 81 years). The specimens were obtained immediately after death and kept deep-frozen until testing. After thawing, a careful dissection was performed leaving the ligaments, joint capsule, and triceps tendon intact. The triceps tendon was left without connection to its muscle. The biceps tendon was removed along with other soft tissues not specified above. The humerus was cut 15 cm from the elbow joint and mounted horizontally in the stress apparatus. The forearm was cut 12 cm from the elbow joint, transfixed in maximum pronation with two threaded pins through the radius and ulna, suspended in a steel cylinder, and placed at the proximal end of a mobile lever arm via two double ball joints. This construction gave firm fixation of the forearm, and during the study no loosening of the pins or the double ball joints was observed. The experimental stress apparatus has been described in detoil." IS. 23 After mounting, the elbow specimens were influenced only by gravity
(0° valgus/varus, 0° rotation, and 90° flexion). In this position the experimental apparatus was calibrated (Figure 1). Three potentiometers were connected at right angles to the mobile arm. One potentiometer registered flexion / extension, another registered valgus/varus, and the third potentiometer registered rotational movements around the axis of the forearm. This axis was the axis of the ulna, because the radius was firmly fixed to ulna. Three pairs of strain gauges mounted in the mobile arm simultaneously recorded the corresponding torque applied to the specimens in the three axes monitored. During testing, data from potentiometers and strain gauges passed through an amplifier that compensated with off-set adjustments for any inaccuracies. One analogue X-Y recorder, which displayed the moment during valgus/varus movement, and a voltmeter, which registered the axial rotational torque (calibrated to 1 V /Newton meter), were coupled to the amplifier. Data were accumulated and stored in a personal computer. During data ac-
J. Shoulder Elbow Surg. Volume 3, Number 3
Olsen et al.
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Ulnar
145
Induced ligament injur y .
collateral ligament (med. coli . lig .)
Anter ior
part
part
Figure 2 Ulnar collateral ligament complex of the elbow joint.
-
Lateral ulnar c ollateral ligament-
Indu ced ligament injur y .
-
-
-
-
-
-
-
-
-
-
-
-
Figure 3 Radial collateral ligament complex of the elbow joint.
quisition the computer display simulta neo usly showed movement curves and indicated the data obtained. This allowed visual control during the test cycle. After the specimens were mounted the stress apparatus was calibrated, and the following test procedures were performed. The specimens were valgus stressed 0.75 Nm during continuous joint flexion from 0° to 140°, and then varus stressed 0.75 Nm during joint extensio n from
140° and back to 0°, Stress was applied manually to the distal pari of the free lever arm. Three complete cycles of elbow movement with stress were carried out to obtain about 500 useful data points. Data were recorded from 10° to 130° of [oint flexion to avoid difficulties with inconsistent data collection at maximum elbow joint extension and flexion . During the movement and moment pdttern described previously, the corresponding spontaneous rotation
J. Shoulder Elbow Surg. May/June 1994
146 Olsen et al.
-
Valgus degrees
Intact Injured
50-
.I . +.
-5-
I
•
-10-
.
-t~
-15--'------------------o 10 20 30 40 50 60 70 80 90 100 110 120 130
Elbow flexion-degrees
Figure 4 Movement curve during valgus stress for intact and injured joi nts. Negative values describe valgus. Values expressed in mean ± SEM (standard error of mean ). * p < 0.02.
-
Valgus stressed spontaneous ulnar rotation -degrees
Intact Injured
15 10
5
o -5 --'-- - - - - - - - - - - - - - - - - -
o 10
20 30
40 50 60 70 80 90 100 110 120 130
Elbow flexion-degrees
Figure 5 Movement curve for spontaneous external rotation around ulnar axis during valgus stress for intact and injured joi nts. Positive values describe external rotation . Values expressed in mean ± SEM. * p < 0.02.
around the ulnar axis of the specimens was also recorded. Then in a cycle, external rotatory torque of 0.75 nm in continuous elbow joint flexion from 00 to 1400 and internol rotatory torque of 0.75 nm in extension from 140 back to 0 were applied to the specimens. Five complete cycles were carried out to obtain about 1000 useful data points. Data were recorded as stated previously. Subsequently both recordings were repeated to test the reproducibility of the measurements. Then total division of the ACL at the insertion on the medial humeral epicondyle (Figure 2) and total division of the LA posterior to the ro0
0
dial collaterol ligament insertion on the lateral humeral epicondyle (Figure 3) was performed . This experimental ligamentous lesion was tested as described previously. Statistically the results for the intact and the matched injured jo int specimens were compared. A paired ttest was applied to the results for each specimen (BMDP Statistical Software Inc., Los Angeles). The results were expressed by the mean and the standard error of the mean (SEM) and were considered significant at p < 0.02. Reproducibility of the measurements was assessed through a series of double recordings. Reproducibility was estimated by calculating
1. Shoulder Elbow Surg.
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01.
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Volume 3, Number 3
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Varus degrees
Intact Injured
15
10
5 I----I--II-~-f_I---f_+--f---iIC---r----iI:---+--If-.--I o-'--------------~----
o
10
20
30
40 50
60
70 80
90 100110120 130
Elbow flexion-degrees
Figure 6 Movement curve during varus stress for intact and injured joints. Positive values describe varus. Values expressed in mean ± SEM. *p 0.02.
-
Varusstressed spontaneous ulnar rotation-degrees
<
Intact Injured
15-
50-
-5-'-------------------
o
10
20
30
40 50
60
70 80
90 100 110 120 130
Elbow flexion-degrees
Figure 7 Movement curve for spontaneous rotation around ulnar axis during varus stress for intact and injured joints. Positive values describe external and negative values internal rotation. Values expressed in mean ± SEM. * p < 0.02.
the difference between the paired mobility patterns at 100 through 1300 of flexion and stated as the standard error of difference (SED).
RESULTS We defined elbow joint subluxation as separation of the radiohumeral and proximal radioulnar articulation with preservation of the humeroulnar articulation. After the medial and lateral ligamentous injury was created subluxation was observed in all the specimens examined while hanging freely, only influenced by gravity (00 valgus/varus, 00 rotation, and 900 flexion).
During valgus stress significant laxity was induced by division of the ligaments (Figures 4 and 5). We found a mean maximum valgus laxity of 5.70 at 500 of joint flexion. The corresponding spontaneous increase in external rotation around the ulnar axis was o mean maximum of 7.3 0 at 60 0 of joint flexion. During varus stress significant laxity was induced by ligament division (Figures 6 and 7). We found a mean maximum varus laxity of 9.9 0 at 80 0 of joint flexion. The corresponding spontaneous increase in external rotation around the ulnar axis was a mean maximum of 6.5 0 at 1000 of joint flexion.
148
Olsen et
01.
J. Shoulder Elbow Surg. May/June 1994
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Forced external rotation-degrees
Intact Injured
25
*
20 15 10 5
O~------------------
o
10
20 30 40 50 60 70 80 90 100 110 120 130
Elbowflexion-degrees
Figure 8 Movement curve forforced external rotation for intact and injured joints. Positive values describe external rotation. Values expressed in mean ± SEM. * p < 0.02.
Forced internal rotation-degrees
-
Intact
-
lnjured,
o -5
-10 _15....1---------"--'---"---------o 10 20 30 40 50 60 70 80 90 100 110 120 130
Elbow flexion-degrees
Figure 9 Movement curve for forced internal rotation for intact and injured joints. Negative values describe internal rotation. Values expressed in mean ± SEM. * p < 0.02.
The measurements for joints stressed in external and internal rotation also showed a significant increase in laxity after creation of the ligament lesions (Figures 8 and 9). In forced external rotation we found a mean maximum increase in joint laxity of 13.2° at 80° of joint flexion. In forced internal rotation there was a mean maximum laxity of 8.9° at 50° of joint flexion. We performed one repetition of all recordings, and the following reproducibility results were estimated. Forthe intact specimens (Table
I) a maximum (SED) of 0.54° was found in forced external rotation at 110° of joint flexion. For the injured specimens (Table II) a maximum (SED) of 1.09° was found in forced internal rotation at 80° of joint flexion.
DISCUSSION Different biomechanical models of the elbow joint have been developed and used." 8. 11. 20 Some examinations of elbow joint stability were performed exclusively in full joint extension." Later studies have, in accordance with our ob-
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Table I Measurement reproducibility for intact joints (standard error of difference, degrees) Elbow flex (degrees) Stress
10
30
50
80
110
130
Valgus Valgus Spon.R Varus Varus Spon.R Ext.R Int.R
0.30 0.19
0.10 0.14
0.13 0.13
0.09 0.13
0.15 0.21
0.23 0.15
0.17 0.15
0.11 0.23
0.11 0.11
0.04 0.18
0.09 0.37
0.18 0.22
0.18 0.17
0.16 0.10
0.17 0.28
0.47 0.41
0.54 0.25
0.43 0.43
Elbow Flex, Elbow joint flexion in degrees; Stress, indicates the direction of stress applied to the one-bone forearm; Spon.R, spontaneous rotation around the ulnar axis during valgus or varus stress, Ext.R, external rotation; Int.R, internal rotation.
Table II Measurement reproducibility for injured joints (standard error of difference, degrees) Elbow flex (degrees) Stress
10
30
50
80
110
130
Valgus Valgus Spon.R Varus Varus Spon.R Ext.R Int.R
0.57 0.27
0.35 0.54
0.23 0.46
0.18 0.51
0.43 0.21
0.41 0.29
0.42 0.36
0.68 0.26
0.38 0.17
0.27 0.70
0.41 0.19
0.20 0.17
0.31 0.42
0.25 0.66
0.62 0.52
1.09 0.32
0.91 0.40
0.54 0.36
Elbow Flex, Elbow joint flexion in degrees; Stress, indicates the direction of stress applied to the one-bone forearm, Spon.R, spontaneous rotation around the ulnar axis during valgus or varus stress, Ext.R, external rotation; Int.R, internal rotation.
servations, shown that stability of the elbow joints in full extension or flexion are less dependent on the collateral ligaments and are primarily dependent on the osseous and articular geometry for their stobility."": 21-23 Many of these models lacked continuous measurements through the complete flexion ore." a. 11.20 Different authors have used the magnetic tracking device": 17 developed by An et ol.' In this model stresses were induced to the specimens through gravity force. Measurements of stability were, as in the present study, studied in the complete flexion orch.": 17 An et ol.' found that the magnetic tracking device is hindered by metallic conductors in the specimens examined. Because metal screws, clamps, and other metal-containing devices may be useful for the reconstruction of joint stability, we consider this to be a problem. In An's model reproducibility tests were performed with a mechanical model.' The present model has exhib-
ited a high degree of reproducibility with an error of approximately 0.5°, equal to the magnetic tracking device. 1. 14 The ligamentous injuries in this kinematic model were induced on the basis of previous studies." 13. 14. 2°- 23 0 ther studies have emphasized different ligamentous and osseous structures as being of importance to elbow constrcint." 13, 14, 17, lain a previous study" severance of the ACL caused a mean maximum valgus laxity of 11.8° at 70° of elbow flexion, with neutral forearm rotation and after application of 1.5 nm stress. The results in the present study averaged only half of this at a joint flexion angle of 50°. Morrey et ol.," during gravity valgus stress and forearm supination, induced a complete lesion of the medial collateral ligament, removed the radial head, and observed an external rotational laxity of 10° to 11 ° between 30° to 100° of joint flexion. This seems compatible with our observations. In a study" carried out
150 Olsen et al.
in our laboratory, the LA was divided, and a mean maximum varus laxity of 13.7° was found with elbow flexion of 60°. The conditions for stress and forearm rotation were as described previously." This is also in agreement with our results. In forced internal rotation the ACL injury23 induced a mean maximum laxity of 5.4° at 80° of joint flexion. We found a mean maximum laxity of 8.9° at a joint flexion angle of
50°. In the present study a small, well-defined, measurable moment of 0.75 nm was applied to the specimens, because testing of the mechanical strength of the ligaments was not intended. The medial and lateral ligamentous injury was created, avoiding radial head damage, because that is the usual observed injury after traumatic elbow joint disolocotion." 18.22 Preliminary studies led Morrey to conclude that rotation of the forearm did not interfere with observed movement and laxity potterns." We chose to fix the forearm in maximum pronation, because this gave the stability necessary for our recordings. In the present model we were able to record the spontaneous rotation around the ulnar axis during valgus and varus stress. Morrey has measured rotation around the axis of the one-bone forearm during gravity valgus stress." We consider this to be an important biomechanical parameter because of its influence on the humeroulnar articulation. It can be concluded that the present kinematic model of the elbow joint has proven itself to be reproducible and informative. Compared with in vivo conditions, this model is not influenced by the soft tissues other than the collateral ligaments. This was chosen because we wished to test only the static stabilizers. In future studies we will test the biomechanical influence of reconstructive procedures aimed at treating elbow joint instability.
REFERENCES
1. Shoulder Elbow Surg. May/June 7994
3. Josefson PO, Johnell 0, Wenderberg B. Ligamentous injuries in dislocations of the elbow joint. C1in Orthop 1985;221:221-5. 4. Josefson PO. The dislocated elbow. With special reference to incidence, ligamentous injuries and stability. Thesis, University of Lund, Sweden, 1986: 13. 5. Kapel 0. Operation for habitual dislocation of the elbow. J Bone Joint surg [Am] 1951;33A: 707-10. 6. Kjrersgaard-Andersen P, Frich LH, Madsen F, Helmig P, S0gard P, Sejbjerq JO. Instability of the hindfoot after lesions of the ankle ligaments. C1in Orthop 1991; 266: 170-9. 7. linscheid RL, Wheeler DK. Elbow dislocations. JAMA 1965;194:1171-6. 8. London JL. Kinematics of the elbow. J Bone Joint Surg [Am] 1981;63A:529-35. 9. Milch H. Bilateral recurrent dislocation of the ulna at the elbow. J Bone Joint Surg 1936;18:777-80. 10. Morrey BF,Chao EYS. Passivemotion of the elbow joint. J Bone Joint Surg [Am] 1976;58A:501-8. 11. Morrey BF, An KN. Articular and ligamentous contributions to the stability of the elbow joint. Am J Sports Med 1983;11:315-9. 12. Morrey BF,An KN. Functional anatomy of the ligaments of the elbow. On Orthop 1985;201:84-9. 13. Morrey BF, Tanaka S, An KN. Valgus stability of the elbow. C1in Orthop 1991;265:187-95. 14. Nielsen S, Hvid I, Andersen K. Experimental measurement of rotatory and translatory instability of the knee joint. Engineering in Medicine, MEP Ltd, 1985;14:123-6. 15. O'Driscoll SW, Morrey BF, Korinek S, An KN. The pathoanatomy of posterolateral rotatory instability of the elbow. Orthop Trans 1990;14:629-30. 16. O'Driscoll SW, Bell DF, Morrey BF. Posterolateral rotatory instability of the elbow. J Bone Joint Surg [AmI 1991;73A:440-6. 17. O'Driscoll SW, Morrey BF, Korinek S, An KN. Elbow subluxation and dislocation. Clin Orthop 1992;280: 18697. 18. Osborne G, Cotterill P. Recurrent dislocation of the elbow. J Bone Joint Surg [Br] 1966;48B:340-6. 19. Reichenheim PP. Transplantation ofthe bicepstendon as a treatment for recurrent dislocation of the elbow. Br J Surg 1947;35:201-4. 20. Schwab GH, Bennet JB, Woods GW, Tullos HS. Biomechanics of elbow instability: The role of the medial collateral ligament. Clin Orthop 1980;146:42-51. 21. Sejbjerq JO, Ovesen J, Gundorf G. The stability of the elbow following excision of the radial head and transection of the annular ligament. Arch Orthop Trauma Surg 1987;106:248-50.
1. An KN, Jacobsen MC, Berglund LJ, Chao EYS. Application of a magnetic tracking device to kinesiologic studies. J Biomechanics 1988;21:613-20.
22. Sejbjerq JO, Helmig P, Kirersgaard-Andersen P. Dislocation of the elbow: An experimental study of the ligamentous injuries. Orthopedics 1989; 12:461-3.
2. Josefson PO, Johnell 0, Gentz CF. Long term sequela of simple dislocation of the elbow. J Bone Joint Surg [Am] 1984;66A:927-30.
23. Sejbjerq JO, Ovesen J, Nielsen S. Experimental elbow instability after transection of the medial collateral ligament. On Orthop 1987;218: 186-90.
The effect of simultoneous ulnar and radial col/ateral ligament division on the kinematics of the elbow joint is studied in a cadaveric model. Severance of the anterior part of the ulnar col/ateralligament and the annular ligament led to significant elbow joint instability in valgus and varus stress and in forced external and internal rotation. The mean maximum laxity in valgus stress and forced external rotation were 5.7' and 73.7'. The forearms of the elbow joint specimens were transfixed in maximum pronation. During valgus and varus stress the corresponding spontaneous ulnar rotation of the specimens was recorded. The reproducibility of the instability pattern suggests that this model is suitable for evaluating stabilizing procedures aimed at correction of elbow joint instability before these procedures are introduced into patient care. (J SHOULDER ELBOW SURG 7994;3: 743-50.)
The elbow is, except for the shoulder, the most frequently dislocated major [oint." 20 Complications such as reduction in joint movement, pain, and neurologic deficits have been reported. v ' A rare and usually severely disabling complication is chronic elbow joint instability, manifested either as instability to valgus stress or recurrent dislocations of the [oint.' Several operative procedures have been described by different authors for treatment of the chronically unstable elbow [oint." 9. 18. 19 The clinical results reported are good,s· 9. 18. 19 but the basic kinematic influence on the joint and late results of these procedures have not been reported. Elbow joint stability depends on the articular geometry and the soft tissues, including the muscles and the collateral liqornents." Previous studies have shown that the prime ligamentous stabilizer on the ulnar aspect of the elbow joint is the anterior part of the ulnar collateral ligament, (ACL)l1· 12.20.23 whereas the prime stabi-
From the Biomechonics Laboratory, Univers ity of Aarhus. Supported by a grant from The Orthopaedic Scientif ic Foundation, Aarhus. Reprint requests : Ba S. Olsen, MD, Biomechanic Laborato ry, Shoulder and Elbow Cl inic, University of Aarhus, Randersvej 1, DK-8200 Aarhus N , Denmark. Copyright © 1994 by Journal of Should er and Elbow Surgery Board of Trustees. 1058-2746/94/$3.00 + 0 32/1154380
lizer on the radial aspect of the joint is the an nular ligament (LA).l1 · 12.21 The ulnar part of the radial collateral ligament prevents posterolateral rotatory stability of the elbow joint, as described by O'Driscoll et a1. 15 • 16 Josefson" 4 reported in a clinical study that posterior elbow joint dislocation was associated with both medial and lateral ligamentous injury. Sajbierq et ol.," in an experimental study of elbow dislocation, described the simultaneous rupture of the ACL and the LA. Furthermore they claimed that posterolateral dislocation of the elbow could be produced only when a combined valgus and external rotatory torque was applied to the forearm. The object of the present study was to measure the laxity of the elbow joint specimens before and after severance of the prime medial and lateral ligamentous stabil izers , and when doing this to develop a reproducible kinematic elbow joint model, encompassing a well -described range of motion in which significant and reproducible ligamentous joint laxity could be induced. Such a model would allow evaluation of the stabilizing effects of reconstructive procedures aimed at correction of elbow joint instability.
MATERIAL AND METHODS Ten macroscopically normal, male, rightsided, osteoligamentous elbow preparations
143
144 Olsen et 01.
1. Shoulder Elbow Surg. May/June 1994
1
1
Voltmeter '. Potentiometers
Rotational torque
X-V-Recorder Valgus/varus moment ••
~train
Gauges
...
Potentio~eie; • • : •
Figure 1 Experimental apparatus used to test stability of the elbow joint.
were studied. The median age at death of the cadaveric donors was 68 years (range 58 to 81 years). The specimens were obtained immediately after death and kept deep-frozen until testing. After thawing, a careful dissection was performed leaving the ligaments, joint capsule, and triceps tendon intact. The triceps tendon was left without connection to its muscle. The biceps tendon was removed along with other soft tissues not specified above. The humerus was cut 15 cm from the elbow joint and mounted horizontally in the stress apparatus. The forearm was cut 12 cm from the elbow joint, transfixed in maximum pronation with two threaded pins through the radius and ulna, suspended in a steel cylinder, and placed at the proximal end of a mobile lever arm via two double ball joints. This construction gave firm fixation of the forearm, and during the study no loosening of the pins or the double ball joints was observed. The experimental stress apparatus has been described in detoil." IS. 23 After mounting, the elbow specimens were influenced only by gravity
(0° valgus/varus, 0° rotation, and 90° flexion). In this position the experimental apparatus was calibrated (Figure 1). Three potentiometers were connected at right angles to the mobile arm. One potentiometer registered flexion / extension, another registered valgus/varus, and the third potentiometer registered rotational movements around the axis of the forearm. This axis was the axis of the ulna, because the radius was firmly fixed to ulna. Three pairs of strain gauges mounted in the mobile arm simultaneously recorded the corresponding torque applied to the specimens in the three axes monitored. During testing, data from potentiometers and strain gauges passed through an amplifier that compensated with off-set adjustments for any inaccuracies. One analogue X-Y recorder, which displayed the moment during valgus/varus movement, and a voltmeter, which registered the axial rotational torque (calibrated to 1 V /Newton meter), were coupled to the amplifier. Data were accumulated and stored in a personal computer. During data ac-
J. Shoulder Elbow Surg. Volume 3, Number 3
Olsen et al.
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Ulnar
145
Induced ligament injur y .
collateral ligament (med. coli . lig .)
Anter ior
part
part
Figure 2 Ulnar collateral ligament complex of the elbow joint.
-
Lateral ulnar c ollateral ligament-
Indu ced ligament injur y .
-
-
-
-
-
-
-
-
-
-
-
-
Figure 3 Radial collateral ligament complex of the elbow joint.
quisition the computer display simulta neo usly showed movement curves and indicated the data obtained. This allowed visual control during the test cycle. After the specimens were mounted the stress apparatus was calibrated, and the following test procedures were performed. The specimens were valgus stressed 0.75 Nm during continuous joint flexion from 0° to 140°, and then varus stressed 0.75 Nm during joint extensio n from
140° and back to 0°, Stress was applied manually to the distal pari of the free lever arm. Three complete cycles of elbow movement with stress were carried out to obtain about 500 useful data points. Data were recorded from 10° to 130° of [oint flexion to avoid difficulties with inconsistent data collection at maximum elbow joint extension and flexion . During the movement and moment pdttern described previously, the corresponding spontaneous rotation
J. Shoulder Elbow Surg. May/June 1994
146 Olsen et al.
-
Valgus degrees
Intact Injured
50-
.I . +.
-5-
I
•
-10-
.
-t~
-15--'------------------o 10 20 30 40 50 60 70 80 90 100 110 120 130
Elbow flexion-degrees
Figure 4 Movement curve during valgus stress for intact and injured joi nts. Negative values describe valgus. Values expressed in mean ± SEM (standard error of mean ). * p < 0.02.
-
Valgus stressed spontaneous ulnar rotation -degrees
Intact Injured
15 10
5
o -5 --'-- - - - - - - - - - - - - - - - - -
o 10
20 30
40 50 60 70 80 90 100 110 120 130
Elbow flexion-degrees
Figure 5 Movement curve for spontaneous external rotation around ulnar axis during valgus stress for intact and injured joi nts. Positive values describe external rotation . Values expressed in mean ± SEM. * p < 0.02.
around the ulnar axis of the specimens was also recorded. Then in a cycle, external rotatory torque of 0.75 nm in continuous elbow joint flexion from 00 to 1400 and internol rotatory torque of 0.75 nm in extension from 140 back to 0 were applied to the specimens. Five complete cycles were carried out to obtain about 1000 useful data points. Data were recorded as stated previously. Subsequently both recordings were repeated to test the reproducibility of the measurements. Then total division of the ACL at the insertion on the medial humeral epicondyle (Figure 2) and total division of the LA posterior to the ro0
0
dial collaterol ligament insertion on the lateral humeral epicondyle (Figure 3) was performed . This experimental ligamentous lesion was tested as described previously. Statistically the results for the intact and the matched injured jo int specimens were compared. A paired ttest was applied to the results for each specimen (BMDP Statistical Software Inc., Los Angeles). The results were expressed by the mean and the standard error of the mean (SEM) and were considered significant at p < 0.02. Reproducibility of the measurements was assessed through a series of double recordings. Reproducibility was estimated by calculating
1. Shoulder Elbow Surg.
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01.
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Volume 3, Number 3
-
Varus degrees
Intact Injured
15
10
5 I----I--II-~-f_I---f_+--f---iIC---r----iI:---+--If-.--I o-'--------------~----
o
10
20
30
40 50
60
70 80
90 100110120 130
Elbow flexion-degrees
Figure 6 Movement curve during varus stress for intact and injured joints. Positive values describe varus. Values expressed in mean ± SEM. *p 0.02.
-
Varusstressed spontaneous ulnar rotation-degrees
<
Intact Injured
15-
50-
-5-'-------------------
o
10
20
30
40 50
60
70 80
90 100 110 120 130
Elbow flexion-degrees
Figure 7 Movement curve for spontaneous rotation around ulnar axis during varus stress for intact and injured joints. Positive values describe external and negative values internal rotation. Values expressed in mean ± SEM. * p < 0.02.
the difference between the paired mobility patterns at 100 through 1300 of flexion and stated as the standard error of difference (SED).
RESULTS We defined elbow joint subluxation as separation of the radiohumeral and proximal radioulnar articulation with preservation of the humeroulnar articulation. After the medial and lateral ligamentous injury was created subluxation was observed in all the specimens examined while hanging freely, only influenced by gravity (00 valgus/varus, 00 rotation, and 900 flexion).
During valgus stress significant laxity was induced by division of the ligaments (Figures 4 and 5). We found a mean maximum valgus laxity of 5.70 at 500 of joint flexion. The corresponding spontaneous increase in external rotation around the ulnar axis was o mean maximum of 7.3 0 at 60 0 of joint flexion. During varus stress significant laxity was induced by ligament division (Figures 6 and 7). We found a mean maximum varus laxity of 9.9 0 at 80 0 of joint flexion. The corresponding spontaneous increase in external rotation around the ulnar axis was a mean maximum of 6.5 0 at 1000 of joint flexion.
148
Olsen et
01.
J. Shoulder Elbow Surg. May/June 1994
-
Forced external rotation-degrees
Intact Injured
25
*
20 15 10 5
O~------------------
o
10
20 30 40 50 60 70 80 90 100 110 120 130
Elbowflexion-degrees
Figure 8 Movement curve forforced external rotation for intact and injured joints. Positive values describe external rotation. Values expressed in mean ± SEM. * p < 0.02.
Forced internal rotation-degrees
-
Intact
-
lnjured,
o -5
-10 _15....1---------"--'---"---------o 10 20 30 40 50 60 70 80 90 100 110 120 130
Elbow flexion-degrees
Figure 9 Movement curve for forced internal rotation for intact and injured joints. Negative values describe internal rotation. Values expressed in mean ± SEM. * p < 0.02.
The measurements for joints stressed in external and internal rotation also showed a significant increase in laxity after creation of the ligament lesions (Figures 8 and 9). In forced external rotation we found a mean maximum increase in joint laxity of 13.2° at 80° of joint flexion. In forced internal rotation there was a mean maximum laxity of 8.9° at 50° of joint flexion. We performed one repetition of all recordings, and the following reproducibility results were estimated. Forthe intact specimens (Table
I) a maximum (SED) of 0.54° was found in forced external rotation at 110° of joint flexion. For the injured specimens (Table II) a maximum (SED) of 1.09° was found in forced internal rotation at 80° of joint flexion.
DISCUSSION Different biomechanical models of the elbow joint have been developed and used." 8. 11. 20 Some examinations of elbow joint stability were performed exclusively in full joint extension." Later studies have, in accordance with our ob-
1. Shoulder Elbow Surg. Volume 3, Number 3
Olsen et
01. 149
Table I Measurement reproducibility for intact joints (standard error of difference, degrees) Elbow flex (degrees) Stress
10
30
50
80
110
130
Valgus Valgus Spon.R Varus Varus Spon.R Ext.R Int.R
0.30 0.19
0.10 0.14
0.13 0.13
0.09 0.13
0.15 0.21
0.23 0.15
0.17 0.15
0.11 0.23
0.11 0.11
0.04 0.18
0.09 0.37
0.18 0.22
0.18 0.17
0.16 0.10
0.17 0.28
0.47 0.41
0.54 0.25
0.43 0.43
Elbow Flex, Elbow joint flexion in degrees; Stress, indicates the direction of stress applied to the one-bone forearm; Spon.R, spontaneous rotation around the ulnar axis during valgus or varus stress, Ext.R, external rotation; Int.R, internal rotation.
Table II Measurement reproducibility for injured joints (standard error of difference, degrees) Elbow flex (degrees) Stress
10
30
50
80
110
130
Valgus Valgus Spon.R Varus Varus Spon.R Ext.R Int.R
0.57 0.27
0.35 0.54
0.23 0.46
0.18 0.51
0.43 0.21
0.41 0.29
0.42 0.36
0.68 0.26
0.38 0.17
0.27 0.70
0.41 0.19
0.20 0.17
0.31 0.42
0.25 0.66
0.62 0.52
1.09 0.32
0.91 0.40
0.54 0.36
Elbow Flex, Elbow joint flexion in degrees; Stress, indicates the direction of stress applied to the one-bone forearm, Spon.R, spontaneous rotation around the ulnar axis during valgus or varus stress, Ext.R, external rotation; Int.R, internal rotation.
servations, shown that stability of the elbow joints in full extension or flexion are less dependent on the collateral ligaments and are primarily dependent on the osseous and articular geometry for their stobility."": 21-23 Many of these models lacked continuous measurements through the complete flexion ore." a. 11.20 Different authors have used the magnetic tracking device": 17 developed by An et ol.' In this model stresses were induced to the specimens through gravity force. Measurements of stability were, as in the present study, studied in the complete flexion orch.": 17 An et ol.' found that the magnetic tracking device is hindered by metallic conductors in the specimens examined. Because metal screws, clamps, and other metal-containing devices may be useful for the reconstruction of joint stability, we consider this to be a problem. In An's model reproducibility tests were performed with a mechanical model.' The present model has exhib-
ited a high degree of reproducibility with an error of approximately 0.5°, equal to the magnetic tracking device. 1. 14 The ligamentous injuries in this kinematic model were induced on the basis of previous studies." 13. 14. 2°- 23 0 ther studies have emphasized different ligamentous and osseous structures as being of importance to elbow constrcint." 13, 14, 17, lain a previous study" severance of the ACL caused a mean maximum valgus laxity of 11.8° at 70° of elbow flexion, with neutral forearm rotation and after application of 1.5 nm stress. The results in the present study averaged only half of this at a joint flexion angle of 50°. Morrey et ol.," during gravity valgus stress and forearm supination, induced a complete lesion of the medial collateral ligament, removed the radial head, and observed an external rotational laxity of 10° to 11 ° between 30° to 100° of joint flexion. This seems compatible with our observations. In a study" carried out
150 Olsen et al.
in our laboratory, the LA was divided, and a mean maximum varus laxity of 13.7° was found with elbow flexion of 60°. The conditions for stress and forearm rotation were as described previously." This is also in agreement with our results. In forced internal rotation the ACL injury23 induced a mean maximum laxity of 5.4° at 80° of joint flexion. We found a mean maximum laxity of 8.9° at a joint flexion angle of
50°. In the present study a small, well-defined, measurable moment of 0.75 nm was applied to the specimens, because testing of the mechanical strength of the ligaments was not intended. The medial and lateral ligamentous injury was created, avoiding radial head damage, because that is the usual observed injury after traumatic elbow joint disolocotion." 18.22 Preliminary studies led Morrey to conclude that rotation of the forearm did not interfere with observed movement and laxity potterns." We chose to fix the forearm in maximum pronation, because this gave the stability necessary for our recordings. In the present model we were able to record the spontaneous rotation around the ulnar axis during valgus and varus stress. Morrey has measured rotation around the axis of the one-bone forearm during gravity valgus stress." We consider this to be an important biomechanical parameter because of its influence on the humeroulnar articulation. It can be concluded that the present kinematic model of the elbow joint has proven itself to be reproducible and informative. Compared with in vivo conditions, this model is not influenced by the soft tissues other than the collateral ligaments. This was chosen because we wished to test only the static stabilizers. In future studies we will test the biomechanical influence of reconstructive procedures aimed at treating elbow joint instability.
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1. Shoulder Elbow Surg. May/June 7994
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