LCDR Patrick W. Joyner
Luke Wilcox
Travis S. Roth
Charles Leddon
Jeremy Bruce
Ryan Hess
Tim Frerichs
Christopher O’Grady
Charles A. Roth
Bone & Joint/Sports Medicine Institute
Naval Medical Center Portsmouth
620 John Paul Jones Circle
Portsmouth, VA 23708
The Andrews Institute for Orthopaedics & Sports Medicine
1040 Gulf Breeze Parkway
Gulf Breeze, FL 32561
3The University of South Alabama
College of Medicine
Mastin #202
2451 Fillingim Street
Mobile, AL 36617-2238
Corresponding Author:
LCDR Patrick Joyner, MD,MS
Bone and Joint/Sports Medicine Institute
Naval Medical Center Portsmouth
620 John Paul Jones Circle
Portsmouth, VA 23708
757-953-1871 (voice)
1-800-775-2671 (fax)
patrick.joyner@med.navy.mil
Senior Author:
Charles A. Roth, MD
The Andrews Institute for Orthopaedics & Sports Medicine
Suite #204
1040 Gulf Breeze Parkway
Gulf Breeze, FL 32561
850-916-8692 (voice)
850-916-8735 (fax)
boneyardroth@gmail.com
Abstract
Background
Anterior cruciate ligament reconstruction incorporating bone-patella-tendon-bone (BPTB) autograft
is a common surgery in orthopaedics; however, there are numerous complications.
Graft tunnel mismatch, is a condition in which the BPTB autograft or allograft is either too long or short,
and can result in compromised fixation.
This complication may be prevented if the length of the ACL was known prior to surgery.
Calculations that can determine native ACL length have been published, yet can be difficult and cumbersome.
We aim to find a radiographic landmark, on lateral X-ray, which will allow for a simple, easy,
and reproducible method of quantifying native ACL length.
Hypothesis/Purpose
Lateral X-ray landmarks, specifically Blumensaat’s line, will allow for calculation of native ACL length.
Study Design
Retrospective Case Series
Materials & Methods
130 patients (66 male & 64 female), underwent, as a standard part of their knee arthroscopy or
open knee procedure, measurement of their native ACL. Any patient that had a torn ACL or prior reconstruction
was excluded from the study. These native ACL’s where measured percutaneously or open with a spinal needle,
and length recorded. The lengths of the native ACL’s where compared with one lateral X-ray and clinical landmark:
Blumensaat’s line (BL) and patellar ligament (PL), respectively. A mean percent difference (MPD), the mean percent similarity (MPS),
the absolute difference, and a correlation between Blumensaat’s line and the native ACL length (gold standard) where calculated.
Results
The 66 male patients average age was 48.6 years old (15-79), and the 64 females average age was 50.1 years old (15-74).
For the males, the average length of the ACL was 32.5mm, BL was 33.0mm, and the PL was 49.2mm.
The AD between BL and the native ACL was 1.2mm±1.3mm, the MPD 0.9%±2.9, the MPS was 100.9%±2.9, and the correlation coefficient was 0.88
(>0.8 considered excellent). The correlation coefficient between the PL and the native ACL was 0.08 (<0.2 considered poor).
For the females, the average length of the ACL was 30.6mm, BL was 30.3mm, and the PL 44.2mm.
The AD between BL and native ACL was 1.3mm±1.3mm, the MPD was -0.4%±2.8, the MPS was 99.6%±2.8, and the correlation coefficient was
0.84 (>0.8 considered excellent). The correlation coefficient between the PL and native ACL was 0.1 (<0.2 considered poor).
Conclusion
We have demonstrated a poor correlation between the clinical PL length and the length of the native ACL,
in both males and females. Conversely, we found a strong correlation between the length of BL on lateral X-ray and the length
of the native ACL, in both males and females. Additionally, in both males and females, we demonstrated a MPD between the length
of BL and the length of the native ACL to be less than 1%. Our patient population covered a wide range of ages.
Thus, as a general rule, the length of BL on lateral X-ray is equivalent to length of the native ACL.
Clinical Relevance
Easily and reliably knowing the native ACL length in a patient with a torn ACL can help to prevent the complication of
graft tunnel mismatch.
Key Terms
Graft Tunnel Mismatch, Blumensaat’s line, native anterior cruciate ligament length, mean percent similarity, mean percent difference
What is known about the subject
Calculation of the native ACL has been presented in prior research. However, this mathematical formula was cumbersome and not easily remembered. Additionally, the measurements of the native ACL, from which this linear regression formula was caluclated, where obtained by MRI, not grossly.
What this study adds to existing knowledge
Our study demonstrates an easy, reliable, and cost effective method of obtaining the native ACL length in a patient with a torn ACL. The measurements of the native ACL’s in this study where not based on imaging; instead, these measurements where performed grossly, adding further validity to the data. Finally, to our knowledge, the anatomic relationship presented in this paper has never before been documented in the literature.
Introduction
Rupture of the anterior cruciate ligament (ACL) is a common athletic injury with an estimated 100 to 300 thousand reconstructions taking place each year_ENREF_7 . Anterior cruciate ligament reconstruction was first described in 1917 by Ernest W. Hey-Groves. Generally this is a successful procedure; however, surgical reconstruction of the ACL is not without its complications. Graft-tunnel mismatch, in particular, is an intraoperative complication that can compromise fixation of patellar bone-tendon-bone (BTB) grafts.
Bone-tendon-bone grafts for anterior cruciate ligament reconstruction are frequently employed for the ability to reduce post-operative pain and maximize rehabilitation potential. Graft-tunnel mismatch occurs when the tendon length of a BTB graft is either too short or long between the femoral and tibial bone tunnels. Most commonly, the anterior cruciate ligament graft length is too long, resulting in a protrusion of the graft out of the tibial bone tunnel. When the excess protruding bone is subsequently removed, graft fixation can be compromised. Verma et al reported a 13% rate of graft tunnel mismatch overall and 20% rate of mismatch when utilizing patellar BTB allografts. A reliable preoperative determination of native anterior cruciate ligament length could help to minimize such a complication.
Accurately predicting the native ACL length pre-operatively would help to decrease the likelihood of graft tunnel mismatch. Thus, the purpose of this study is to find a measurement on lateral knee X-ray that can be used to accurately determine the length of the native ACL. We hypothesize that either the clinical length of the patellar ligament or the length of the femoral tunnel on lateral X-ray, Blumensaat’s line, will have significant correlation with the length of the intact native ACL.
Materials & Methods
This study is a retrospective chart review, which received IRB approval from our hospital institutional review board.
The inclusion criteria involve patients who underwent a surgical knee procedure that did not involve treatment of the ACL, had an intact anterior cruciate ligament, and had knee x-rays as part of the pre-surgical assessment within 12 months of the procedure. The exclusion criteria include any patient that had a prior ACL reconstruction or injury, prior surgical procedure or injury to the patellar ligament, and did not have a recent lateral knee X-Ray within 12 months of the procedure.
138 total charts where reviewed. 130 patients had corresponding lateral X-rays. All measurements where done by the primary and senior author. Measurements were performed arthroscopically, 126/138, and in some open procedures, 12/138. All native ACL length was measured in-line with the ligament with the knee at 90° of flexion. In the arthroscopic procedures the measurement was performed percutaneously whereas in the open procedures, the exact same technique was performed grossly. A spinal needle was inserted on top of the ACL until it reached the origin on the medial aspect of the lateral femoral condyle (Fig. 1). The spinal needle was then scored with a grasper, at the insertion of the ACL on the tibia, and the distance from tip of needle to the score was measured (Fig. 2).
The patellar ligament was measured pre-operatively, after anesthesia was administered, with the knee at 90° flexion. This was a clinical measurement, from the distal pole of the patella to the proximal aspect of the tibial tubercle.
Only one radiographic landmark was measured, the depth of the femoral notch; this is commonly referred to as Blumensaat’s line (Fig. 3). We measured this on all patients that had pre-operative lateral X-rays. All X-ray measurements where performed using the GE Centricity® system.
Statistical analysis was performed for males and females only. The absolute difference, mean percent difference, mean percent similarity, and correlation where calculated for the native ACL and Blumensaat’s line; whereas, only a correlation was calculated for native ACL and patellar ligament length. Absolute difference represents the difference between the native ACL and Blumensaat’s line, regardless if longer or shorter. Mean percent similarity represents the similarity of Blumensaat’s line length to the gold standard, the native ACL length. A perfect match is 100%. The mean percent difference represents any number greater or smaller than 100%; the percentage difference between the native ACL length and Blumensaat’s line length. Correlation of >0.8 was considered excellent; whereas, a correlation of <0.2 was considered poor.
Results
A total of 138 patient measurements where obtained; however, only 130/138 (94.2%) had corresponding lateral X-ray. 66/71 (93%) males and 64/67 (95.5%) females had pre-operative lateral X-rays prior to index procedure. Patient demographics are presented in Table 1.
Our results are reported for males and females. Table 2 demonstrates our results as they pertain to overall average native ACL length, Blumensaat’s line length, patellar ligament length, and the absolute difference between the native ACL length and Blumensaat’s line length. Additionally, in Table 3, the mean percent difference and correlation are demonstrated; with the mean percent similarity in Figure 4.
If the native ACL length and Blumensaat’s line length where identical then the absolute difference would be 0mm. We demonstrate an absolute difference of native ACL length and Blumensaat’s line to be 1.2±1.3mm and 1.3±1.3mm in male and females, respectively.
The mean percent difference of native ACL length versus Blumensaat’s line length is 0.9%±2.9 in males and -0.4%±2.8 in females. Thus, the length of Blumensaat’s line is 0.9% longer than the native ACL length in males and 0.4% shorter in females. The correlation between native ACL length and Blumensaat’s line length in males and females is 0.88 and 0.84, respectively. The correlation between native ACL length and patellar ligament length is 0.08 in males and 0.10 in females (Table 3).
The mean percent similarity of the native ACL length compared to Blumensaat’s line length is 100.9%±2.9 in males and 99.6%±2.8 in females. If the two lengths where identical, the means percent similarity would be 100% (Fig. 4).
Discussion
The mean absolute difference between the native ACL length and the length of Blumensaat’s line is 0.9% in males and -0.4% in females. Additionally, the absolute difference in native ACL length compared to Blumensaat’s line in male and females is 1.2mm and 1.3mm, respectively. Therefore, our results demonstrate that the length of Blumensaat’s line on lateral X-ray is virtually equivalent to the length of the native ACL.
To our knowledge, this is the first time that this anatomic relationship has been documented; the roof of the intercondylar fossa is the virtually equivalent to the length of the ACL. However, others have attempted to predict the native length of the ACL previously.
Brown et al examined 414 knee MRI’s with intact ACL’s and developed a linear regression formula to calculate the length of the ACL based on the individuals height. This formula was calculated using the lengths of native ACL’s, as measured on MRI; not ACL lengths measured grossly.
Furthermore, we demonstrate a strong correlation between native ACL length and Blumensaat’s line length. In males our correlation coefficient was 0.88 and in females 0.84. However, we demonstrated a poor correlation between native ACL length and patellar ligament length; 0.08 and 0.l0 in males and females, respectively. Denti et al examined 50 knees endoscopically and 9 cadaver knees and demonstrated no statistically significant correlation between native ACL and patellar ligament length.
One strength of our study is that we did not use MRI; instead, we measured the native length of the ACL grossly. MRI quality can be affected by the strength of the magnet; as a result, a poor quality MRI could affect the measurement of the ACL. Additionally, it is not cost-effective to repeat an MRI. However, X-rays are consistent in quality, and if one requires replication, the additional cost is minimal when compared to a MRI. Furthermore, by measuring the native ACL length grossly, we feel this native ACL length is more valid than the length of an ACL measured off an image.
Another strength of our study is that we did not group our data together; instead reported our results as they regard to males and females. It has been demonstrated that a narrow femoral notch is a risk factor for ACL injury; and that woman have a more narrow notch than men. Therefore, examining the data by sex, we could determine if there are any differences between femoral notch depth in males and females and native ACL length.
A limitation of our study is that our data is collected retrospectively. However, by obtaining the length of the native ACL first, and subsequently the length of Blumensaat’s line; we eliminated measurement bias.
A second limitation of the study is our method for native ACL length acquisition. Albeit grossly, a majority of the native ACL length measurements where performed percuatneoulsy. Therefore, we feel our measurement is best representative of the anteromedial bundle of the ACL. To determine how this pertains to the length of the reconstructed ACL will require additional research. However, we feel all of our measurements reflect the distance of the native ACL from the femoral origin to the Tibial insertion.
The use of the central third of the patellar ligament has been described as a viable graft choice for ACL reconstruction; however it is not without complications. Graft-tunnel mismatch occurs when the tendon length of a BPTB graft is either too short or too long between the femoral and tibial bone tunnels. The use of allografts as well as an autograft in a patient with patella baja or alta can increase the likelihood of graft tunnel mismatch.
Our study is the first to demonstrate the length of the native intact ACL is virtually the same the length as Blumensaat’s line. Further research will help to determine how this information can help reduce the complication of the graft tunnel mismatch.
Conclusion
As a general rule, regardless of age and sex, the length of Blumensaat’s line is equal to the length of the intact native anterior cruciate ligament.
References
- Auge WK, 2nd, Yifan K. A technique for resolution of graft-tunnel length mismatch in central third bone-patellar tendon-bone anterior cruciate ligament reconstruction. Arthroscopy. 1999;15(8):877-881.
- Barber FA. Flipped patellar tendon autograft anterior cruciate ligament reconstruction. Arthroscopy. 2000;16(5):483-490.
- Brown JA, Brophy RH, Franco J, et al. Avoiding allograft length mismatch during anterior cruciate ligament reconstruction: patient height as an indicator of appropriate graft length. Am J Sports Med. 2007;35(6):986-989.
- Clancy WG, Jr. Intra-articular reconstruction of the anterior cruciate ligament. Orthop Clin North Am. 1985;16(2):181-189.
- Clancy WG, Jr., Nelson DA, Reider B, Narechania RG. Anterior cruciate ligament reconstruction using one-third of the patellar ligament, augmented by extra-articular tendon transfers. J Bone Joint Surg Am. 1982;64(3):352-359.
- Denti M, Bigoni M, Randelli P, et al. Graft-tunnel mismatch in endoscopic anterior cruciate ligament reconstruction. Intraoperative and cadaver measurement of the intra-articular graft length and the length of the patellar tendon. Knee Surg Sports Traumatol Arthrosc. 1998;6(3):165-168.
- Fowler BL, DiStefano VJ. Tibial tunnel bone grafting: a new technique for dealing with graft-tunnel mismatch in endoscopic anterior cruciate ligament reconstruction. Arthroscopy. 1998;14(2):224-228.
- Getelman MH, Friedman MJ. Revision anterior cruciate ligament reconstruction surgery. J Am Acad Orthop Surg. 1999;7(3):189-198.
- Hartman GP, Sisto DJ. Avoiding graft-tunnel mismatch in endoscopic anterior cruciate ligament reconstruction: a new technique. Arthroscopy. 1999;15(3):338-340.
- Hey-Groves EW. The Use of Fascial and Tendon Grafts in Certain Fractures and Dislocations. Ann Surg. 1934;100(1):20-29.
- Jacobsen K, Bertheussen K, Gjerloff CC. Characteristics of the line of Blumensaat. An experimental analysis. Acta Orthop Scand. 1974;45(5):764-771.
- Jones KG. Reconstruction of the Anterior Cruciate Ligament. A Technique Using the Central One-Third of the Patellar Ligament. J Bone Joint Surg Am. 1963;45:925-932.
- Macaulay AA, Perfetti DC, Levine WN. Anterior cruciate ligament graft choices. Sports Health. 2012;4(1):63-68.
- Pace A, Fergusson C. Preoperative computerized radiograph measurement of Blumensaat's line as an aid to correct placement of the femoral tunnel in ACL reconstruction. J Knee Surg. 2006;19(3):176-180.
- Shaffer B, Gow W, Tibone JE. Graft-tunnel mismatch in endoscopic anterior cruciate ligament reconstruction: a new technique of intraarticular measurement and modified graft harvesting. Arthroscopy. 1993;9(6):633-646.
- Soher BJ, Dale BM, Merkle EM. A review of MR physics: 3T versus 1.5T. Magn Reson Imaging Clin N Am. 2007;15(3):277-290, v.
- Uhorchak JM, Scoville CR, Williams GN, Arciero RA, St Pierre P, Taylor DC. Risk factors associated with noncontact injury of the anterior cruciate ligament: a prospective four-year evaluation of 859 West Point cadets. Am J Sports Med. 2003;31(6):831-842.
- Verma NN, Dennis MG, Carreira DS, Bojchuk J, Hayden JK, Bach BR, Jr. Preliminary clinical results of two techniques for addressing graft tunnel mismatch in endoscopic anterior cruciate ligament reconstruction. J Knee Surg. 2005;18(3):183-191.
- Yang X, Holmes MJ, Newton AT, Morgan VL, Landman BA. A Comparison of Distributional Considerations with Statistical Analysis of Resting State fMRI at 3T and 7T. Proc Soc Photo Opt Instrum Eng. 2012;8314.
Figures
Figure 1: Arthroscopic view of percutaneous spinal needle at origin of ACL on medial aspect of the lateral femoral condyle.
Figure 2: Arthroscopic view of percutaneous spinal needle at insertion of ACL on tibia.
Fig. 3: Measurement of femoral notch, Blumensaat’s line, on lateral X-ray.
Figure 4: MPS nACL/BL = mean percent similarity between native ACL length and Blumensaat’s line length.
Tables
|
Male |
Female |
| n |
66 |
64 |
| Age Range |
15-79 |
15-73 |
| Mean Age |
48.6 |
50.1 |
| <18 |
8 |
5 |
| >65 |
11 |
12 |
Table 1: Patients demographics by sex.
|
Male |
Female |
| ave. nACL |
32.5 |
30.6 |
| ave. BL |
33 |
30.3 |
| ave. PL |
49.2 |
44.2 |
| AD nACL/BL _ENREF_7 |
1.2 |
1.3 |
Table 2: ave. nACL = average native ACL length, ave. BL = average Blumensaat’s line length, ave. PL = average patellar ligament length, AD nACL/BL = absolute difference between native ACL length and Blumensaat’s line length.
|
Male |
Female |
| MPD nACL/BL (%) |
0.9 |
-0.4 |
| Corr nACL/BL |
0.88 |
0.84 |
| Corr nACL/PL |
0.08 |
0.10 |
Table 3: MPD nACL/BL = mean percent difference of native ACL length compared to Blumensaat’s line length, Corr nACL/BL = correlation coefficient of native ACL length compared to Blumensaat’s line length, Corr nACL/PL = correlation coefficient of native ACL length compared to patellar ligament length.