Influence of knee flexion and femoral cross-pin insertion angle on posterolateral structures of the knee and lateral fixation lengths during ACL reconstruction

ORIGINAL ARTICLE

Influence of knee flexion and femoral cross-pin insertion angleon posterolateral structures of the knee and lateral fixation lengthsduring ACL reconstruction

Jin Goo Kim • Yong Seuk Lee • Jeong Ku Ha •

Sung Soo Jun • Young Jin Chang

Received: 23 May 2011 / Accepted: 9 December 2011 / Published online: 11 January 2012

� Springer-Verlag 2012

Abstract

Purpose Some studies have investigated knee flexion

angle on the sagittal plane and insertion angle of the cross-

pin on the coronal plane to evaluate proper femoral

fixation. They evaluated the possibilities of injury to the

posterolateral (PL) and neurovascular structures using

several methods. The purposes of this study were to eval-

uate (1) the influence of knee flexion and femoral cross-pin

insertion angles on knee PL structures and (2) the lateral

fixation length of the cross-pin.

Methods Ten fresh cadaveric knees with no previous

surgeries around the knee were used. Transtibial femoral

tunnels (1:30 or 10:30 o’clock position) were made at three

different knee flexion angles (70�, 90�, and 110�). Two

cross-pin guidewires (superior and inferior pins) were

drilled at three different insertion angles [downward 30�, 0�(parallel to floor line), and upward 30�] for each knee

flexion position. The distances from the insertion point of

the two cross-pins to the lateral collateral ligament (LCL)

and popliteus tendon (PT), and the distance from the lateral

wall of the femoral tunnel to the lateral cortex of the

femoral condyle were measured.

Results No significant differences were observed in the

superior and inferior pin depths (p = 0.56 and 0.39). The

distances from the superior pin to the LCL and from the

inferior pin to the LCL were significantly shorter in all

knee flexions with 0� and an upward 30� insertion angle

than with 70� and 90� knee flexion with a downward 30�insertion angle, respectively (superior pin: p = 0.02 and

0.03; inferior pin: p = 0.03 and 0.03). No significant dif-

ference was observed in the distance between the superior

pin and inferior pins and the PT (p = 0.25).

Conclusions The cross-pin was inserted close to the LCL

and PT, and a downward 30� angle was the safest insertion

angle. Lateral fixation length was sufficient for the cross-

pin fixation in the 10:30- or 1:30-positioned femoral tunnel.

Keywords Anterior cruciate ligament � Lateral collateral

ligament � Popliteus tendon � Fixation � Cross-pin

Introduction

Soft tissue grafts for anterior cruciate ligament (ACL)

reconstruction are widely used, and femoral cross-pin fixa-

tion is accepted as a good alternative option [1, 10, 11].

However, several factors must be considered during femoral

fixation using this device. Fixation length (the distance from

the lateral wall of the femoral tunnel to the lateral cortex of

the femoral condyle) must be sufficient, and too short a fix-

ation length must be avoided to obtain strong femoral fixa-

tion. Additionally, the possibility of posterolateral (PL)

structural and neurovascular injury must be considered.

Some studies have investigated knee flexion angle on the

sagittal plane and insertion angle of the cross-pin on the

coronal plane to evaluate proper femoral fixation. They

evaluated the possibilities of injury to the PL and

J. G. Kim � J. K. Ha

Department of Orthopedic Surgery, Seoul Paik Hospital,

Inje University, Seoul, Korea

Y. S. Lee (&) � S. S. Jun

Department of Orthopedic Surgery,

Gachon University School of Medicine, Gil Hospital,

117, Yong-dong, Jung-gu, Incheon 400-713, Korea

e-mail: [email protected]

Y. J. Chang

Department of Anesthesiology and Pain Medicine,

Gil Medical Center, Gachon University of Medicine

and Science, Incheon, Korea

123

Surg Radiol Anat (2012) 34:421–425

DOI 10.1007/s00276-011-0922-7

neurovascular structures using several methods [2, 9, 11–13].

However, these studies evaluated only one specific condition

such as knee flexion [2, 9], cross-pin insertion angle [11], or

the tunneling method for the femoral side (transtibial or

anteromedial portal technique) [13]. McKeon et al. [11].

suggested that the safest zone for the prevention of neuro-

vascular injury during cross-pin guidewire placement was

from downward 20� to upward 40�, whereas Basdekis et al.

[2]. indicated that the optimal angle of knee flexion was 110�because the 90� pin was close to the posterior wall, resulting in

a short tunnel. Also, 130� of knee flexion is associated with

high tunnel acuity [2]. However, it is possible for these safe

knee flexion and cross-pin insertion angles to be dangerous for

the PL structures at the insertion area of the cross-pin.

The purposes of this study were to (1) evaluate the

influence of knee flexion and femoral cross-pin insertion

angles on knee PL structures and (2) evaluate the change in

lateral fixation length of the cross-pin based on various

combinations of knee flexion and femoral cross-pin inser-

tion angles. The hypotheses of this study were that some

knee flexion and cross-pin insertion angles cause PL

structural injury and that the lateral fixation length is too

short for cross-pin fixation under certain conditions.

Materials and methods

Ten fresh cadaveric knees with no previous surgeries

around the knee were used. Specimens were thawed at

room temperature 48 h before the experiment. Soft tissues

were dissected until the lateral collateral ligament (LCL)

and popliteus tendon (PT) were identified. Medial struc-

tures were preserved, and the patellar tendon was removed.

A tibial tunnel (8 mm diameter) was made with an ACL

tibial guide (Linvatec, Largo, FL, USA) set at a 45� angle,

and a femoral tunnel was made at a 10:30 position for the

right knee and at a 1:30 position for the left knee with a

femoral guide using a 6-mm over-the-top guide through the

transtibial tunnel. Three femoral tunnels were made at

three different knee flexion angles (70�, 90�, and 110�)

using a single tibial tunnel (Fig. 1). The cross-pin guide

was inserted sequentially into three different femoral tun-

nels, and two cross-pin guidewires (superior and inferior

pin) were drilled at three different insertion angles

[downward 30�, 0� (parallel to the floor line), and upward

30�] for each knee flexion position using a goniometer

(Fig. 2). The shortest distances from the insertion point of

the two cross-pins to the LCL and PT were measured using

calipers. The distance from the lateral wall of the femoral

tunnel to the lateral cortex of the femoral condyle was

measured using a depth gauge. A total of six guide pins

were inserted.

A power analysis was performed. If a difference of more

than 5 mm was observed, we believed it would be clini-

cally significant. The alpha level was 0.05, the power was

0.8, and the standard deviation of the distance was 3. The

reliability of the measurements was assessed by examining

intra- and interrater reliability using the intraclass

Fig. 1 Femoral tunnels (1:30 or 10:30 o’clock position) were made at three different knee flexion angles [70� (a), 90� (b), and 110� (c)]

Fig. 2 Two cross-pins were drilled at three different insertion angles [downward 30� (a), 0� transverse (b), and upward 30� (c)] for each knee

flexion position

422 Surg Radiol Anat (2012) 34:421–425

123

correlation coefficient (ICC). Two orthopedic surgeons

measured the distance with calipers. The Kruskal–Wallis

test with a post hoc Conover test was used with Medcalc

11.0 (MedCalc, Mariakerke, Belgium). p values of \0.05

were considered to be significant.

Results

The required sample size was six cases. The power was

96% with ten cadavers. The inter- and intrarater reliabili-

ties ranged from 0.82 to 0.91. No significant differences in

the superior and inferior pin depths were observed among

preparations (p = 0.56 and 0.39, respectively). However,

the distance from the superior pin to the LCL was signif-

icantly different (p \ 0.01) between ranks 1–4 and ranks

7–10 (Table 1; groups ranked according to outcome). The

distance from the inferior pin to the LCL was significantly

different (p \ 0.01) between ranks 1–2 and ranks 4–9

(Table 2; groups ranked according to outcome). No sig-

nificant difference was observed among groups in the

distance between the superior pin and the PT (p = 0.25)

(Table 3; groups ranked according to outcome). The dis-

tance from the inferior pin to the PT was significantly

different (p \ 0.01) between rank 1 and ranks 3–9

(Table 4; groups ranked according to outcome).

Regarding statistical risk group, 70�, 90�, and 110�flexion were counted as 5, 5, and 5 groups, respectively

(p = 0.84). Downward 30�, 0� transverse, and upward 30�were counted as 1, 8, and 7 groups (p \ 0.01). Among nine

groups, 70� knee flexion–0� transverse and 90� knee flex-

ion–0� transverse insertion groups were included in risky

group in all statistically significant measurements. Among

the nine groups, the 70� knee flexion–0� transverse inser-

tion and the 90� knee flexion–0� transverse insertion

groups were identified as high-risk groups in all measures

of statistical significance (p \ 0.05).

Discussion

The principle findings of our study were that the safest pin

insertion angle was downward 30�, and the most dangerous

combinations were 70� knee flexion–0� pin insertion and

90� knee flexion–0� pin insertion. The safety of the PL

structure was not different according to the knee flexion

angle. The lateral fixation length was long enough for

Table 4 Distance from the inferior cross-pin to the popliteus

Rank Knee position–insertion angle (�) Mean (mm) SD

1 70 flexion–30 downward 10.4 2.6


3 110 flexion–30 upward 5.9 5


5 90 flexion–30 upward 4 4.1

6 70 flexion–30 upward 2.9 3

7 110 flexion–0 transverse 2.9 4

8 90 flexion–0 transverse 2.7 2.3


Table 1 Distance from the superior cross-pin to the lateral collateral

ligament




3 110 flexion–30 downward 12.1 3

4 110 flexion–30 upward 10.1 6.1



7 110 flexion–0 transverse 5.4 4



Table 2 Distance from the inferior cross-pin to the lateral collateral

ligament







6 110 flexion–30upward 5.4 3.5




Table 3 Distance from the superior cross-pin to the popliteus



2 90 flexion–30 downward 13.3 4

3 110 flexion –30 upward 12.7 5.5

4 90 flexion –30 upward 12.4 7.3






Surg Radiol Anat (2012) 34:421–425 423

123

cross-pin fixation in the 10:30- or 1:30-positioned femoral

tunnel. The distance from the LCL was close at the prox-

imal one-third of the LCL. The distance from the popliteus

was close at the distal tendinous portion with a 30�downward and 0� transverse insertion, but at the proximal

muscular portion or musculotendinous junction, it was

close with a 30� upward insertion. The lateral fixation

length was sufficient because the pin was inserted near the

lateral epicondyle, which is more prominent than the lateral

cortex.

When the femoral tunnel was drilled through the

anteromedial portal for ACL reconstruction, the knee

flexion angle influenced the femoral drilling position, and a

110� knee flexion position was optimum, whereas a 90�flexion resulted in a short tunnel that was too close to the

posterior wall. A knee flexion of 130� is associated with

high tunnel acuity and, because maximum flexion is quite

variable from one knee to another, it cannot be recom-

mended [2]. However, Pujol et al. [13]. reported that the

use of an anteromedial portal was associated with the risk

of an LCL iatrogenic lesion close to the femoral insertion,

and this risk can clearly be reduced with correct tunnel

depth and maximum knee flexion during surgery. McKeon

et al. [11]. reported that the absolute neurovascular safe

zone during cross-pin guidewire placement is from down-

ward 20� to upward 40�. These results, combined with our

series, imply that no perfect combination of knee flexion

and insertion angle exists that satisfactorily addresses all

concerns (for example, tunnel length, lateral fixation

length, graft acuity, safety for the posterior neurovascular

and PL structures).

The risk of cartilage injury is highly reported with an

anteromedial portal technique using a cross-pin [3, 4]. In

addition, some problems have been reported [5–8]. We

have treated some patients who have vague pain at the

posterolateral side of the knee after ACL reconstruction

using femoral cross-pins, although they did not complain

preoperatively of pain in this area. This suggests that the

pain might be associated with a PL structural injury. In

addition, according to Yan et al. [14], the innervations of

the two membranes on the surface of LCL may be asso-

ciated with an indistinct pain. They clarified the innerva-

tion pattern of LCL using 55 cadaveric knees.

Our study had several limitations. First, the experiment

was performed with a single technique. However, we used

common graft diameter (8 mm), tunneling position (10:30

and 1:30), and a femoral side method (transtibial tech-

nique) because we could not investigate all conditions.

Second, we could not demonstrate the negative conse-

quences of the small cross-pin insertion, because it pierced

the PL structure and did not protrude to the outside of the

cortex. Third, we cannot recommend a perfect angle that

satisfactorily addresses all concerns. Fourth, we cannot

define the absolute values of safe angle and distance. We

only assumed that it was risky if the distance was close to

the PL structures and it was only a relative value by

comparison of some conditions.

Conclusion

The cross-pin was inserted close to the LCL and PT, and a

downward 30� angle was the safest for insertion. Lateral

fixation length was sufficient for cross-pin fixation with a

10:30- or 1:30-positioned femoral tunnel.

Conflict of interest We declare that we have no conflict of interest.

References

1. Ahn JH, Park JS, Lee YS, Cho YJ (2007) Femoral bioabsorbable

cross-pin fixation in anterior cruciate ligament reconstruction.

Arthroscopy 23:1093–1099

2. Basdekis G, Abisafi C, Christel P (2008) Influence of knee flexion

angle on femoral tunnel characteristics when drilled through the

anteromedial portal during anterior cruciate ligament recon-

struction. Arthroscopy 24:459–464

3. Castoldi F, Bonasia DE, Marmotti A, Dettoni F, Rossi R (2008)

ACL reconstruction using the Rigidfix femoral fixation device via

the anteromedial portal: a cadaver study to evaluate chondral

injuries. Knee Surg Sports Traumatol Arthrosc 16:275–278

4. Chang CB, Yoo JH, Chung BJ, Seong SC, Kim TK (2010)

Oblique femoral tunnel placement can increase risks of short

femoral tunnel and cross-pin protrusion in anterior cruciate lig-

ament reconstruction. Am J Sports Med 38:1237–1245

5. Chen NC, Boykin RE, Millett PJ (2007) Broken femoral cross-

pin after hamstring anterior cruciate ligament reconstruction: case

report. J Knee Surg 20:245–248

6. Choi NH, Lee JH, Victoroff BN (2007) Do broken cross-pins

compromise stability after anterior cruciate ligament reconstruc-

tions with hamstring tendons? Arthroscopy 23:1334–1340

7. Cossey AJ, Paterson RS (2005) Loose intra-articular body fol-

lowing anterior cruciate ligament reconstruction. Arthroscopy

21:348–350

8. Han I, Kim YH, Yoo JH, Seong SC, Kim TK (2005) Broken

bioabsorbable femoral cross-pin after anterior cruciate ligament

reconstruction with hamstring tendon graft: a case report. Am J

Sports Med 33:1742–1745

9. Hoshino Y, Nagamune K, Yagi M et al (2009) The effect of intra-

operative knee flexion angle on determination of graft location in

the anatomic double-bundle anterior cruciate ligament recon-

struction. Knee Surg Sports Traumatol Arthrosc 17:1052–1060

10. Jung YB, Nam CH, Jung HJ, Lee YS, Ko YB (2009) The influ-

ence of tibial positioning on the diagnostic accuracy of combined

posterior cruciate ligament and posterolateral rotatory instability

of the knee. Clin Orthop Surg 1:68–73

11. McKeon BP, Gordon M, DeConciliis G, Scheller A (2007) The

safe zone for femoral cross-pin fixation: an anatomical study.

J Knee Surg 20:285–288

12. Nishimoto K, Kuroda R, Mizuno K et al (2009) Analysis of the

graft bending angle at the femoral tunnel aperture in anatomic

double bundle anterior cruciate ligament reconstruction: a com-

parison of the transtibial and the far anteromedial portal tech-

nique. Knee Surg Sports Traumatol Arthrosc 17:270–276

424 Surg Radiol Anat (2012) 34:421–425

123

13. Pujol N, David T, Bauer T, Hardy P (2006) Transverse femoral

fixation in anterior cruciate ligament (ACL) reconstruction with

hamstrings grafts: an anatomic study about the relationships

between the transcondylar device and the posterolateral structures

of the knee. Knee Surg Sports Traumatol Arthrosc 14:724–729

14. Yan J, Sasaki W, Hitomi J (2010) Anatomical study of the lateral

collateral ligament and its circumference structures in the human

knee joint. Surg Radiol Anat 32:99–106

Surg Radiol Anat (2012) 34:421–425 425

123

Documents

Influence of knee flexion and femoral cross-pin insertion angle on posterolateral structures of the knee and lateral fixation lengths during ACL reconstruction