Foot & Ankle International - September 2020 - 1045

Holzgrefe et al	

1045

Table 3.  Univariable Logistic Regression for Return to Play (RTP) vs Isokinetic Strength Score (ISS): Return to Same Level of Play
(Tegner Δ=0).
Outcome
Population
All
Preinjury Tegner ≥7
Preinjury Tegner <7
Age ≤ 35 y
Age >35 y

n (No. of
patients) RTP n RTP %
36
20
16
19
17

11
5
6
7
4

30.6
25.0
37.5
36.8
23.5

Predictor

Outcomea

Predictive
variable

Level

Regression
coefficient ± SE

OR (95% CI)

P value

RTP (Tegner Δ=0)
RTP (Tegner Δ=0)
RTP (Tegner Δ=0)
RTP (Tegner Δ=0)
RTP (Tegner Δ=0)

ISS
ISS
ISS
ISS
ISS

Per 16 ↑ (1 SD)
Per 16 ↑ (1 SD)
Per 16 ↑ (1 SD)
Per 16 ↑ (1 SD)
Per 16 ↑ (1 SD)

0.0356 ± 0.0258
0.1320 ± 0.0687
0.0066 ± 0.0300
0.0330 ± 0.0326
0.0401 ± 0.0437

1.77 (0.79, 3.97)
8.26 (0.96, 71.23)
1.11 (0.43, 2.84)
1.7 (0.61, 4.72)
1.9 (0.48, 7.48)

.17
.055
.83
.31
.36

Abbreviations: CI, confidence interval; ISS, Isokinetic Strength Score; OR, odds ratio; RTP, return to play; SD, standard deviation; SE, standard error.
a
The return to preinjury level of play outcome was dichotomized and defined based on the change in the Tegner activity scale (Δ Tegner = 0 vs ǂ 0 and Δ Tegner = 0 or −1
vs −2 or −3).

Table 4.  Univariable Logistic Regression for Return to Play (RTP) vs Isokinetic Strength Score (ISS): Return to Within 1 Level of Play
(Tegner Δ=0 or −1).
Outcome
Population
All
Preinjury Tegner ≥7
Preinjury Tegner <7
Age ≤ 35 y
Age >35 y

n (No. of
patients) RTP n RTP %
36
20
16
19
17

21
 7
14
11
10

58.3
35.0
87.5
57.9
58.8

Predictor

Outcomea

Predictive
variable

RTP (Tegner Δ=0 or −1)
RTP (Tegner Δ=0 or −1)
RTP (Tegner Δ=0 or −1)
RTP (Tegner Δ=0 or −1)
RTP (Tegner Δ=0 or −1)

ISS
ISS
ISS
ISS
ISS

Level

Regression
coefficient ± SE

Per 16 ↑ (1 SD) 0.0158 ± 0.0213
Per 16 ↑ (1 SD) 0.1146 ± 0.0567
Per 16 ↑ (1 SD) −0.0183 ± 0.0465
Per 16 ↑ (1 SD) 0.0385 ± 0.0316
Per 16 ↑ (1 SD) −0.0065 ± 0.0307

OR (95% CI)

P value

1.29 (0.66, 2.51)
6.26 (1.06, 37.04)
0.75 (0.17, 3.21)
1.85 (0.69, 4.99)
0.9 (0.35, 2.36)

.46
.043
.69
.22
.83

Abbreviations: CI, confidence interval; ISS, Isokinetic Strength Score; OR, odds ratio; RTP, return to play; SD, standard deviation; SE, standard error.
a
The return to preinjury level of play outcome was dichotomized and defined based on the change in the Tegner activity scale (Δ Tegner = 0 vs ǂ 0 and Δ Tegner = 0 or −1
vs −2 or −3).

rupture. Literature from another common sports injury, anterior cruciate ligament tears, has demonstrated that return to
preinjury sporting activities and higher function following
ACL reconstruction is correlated with increased postoperative
quadricep and hamstring strength.8,10,17,42 Thus, we hypothesized that increased ankle strength would similarly correlate
with return to previous level of sporting activity following
operative repair of an Achilles tendon rupture.
The current study found that at a mean 1.8 years postoperatively from operative repair of the Achilles tendon, 31%
of patients had returned to their previous preinjury level of
play as determined by the Tegner Activity Level Scale and
58% had returned to within 1 Tegner level of play. It should
be noted that this objective scale was not used to define
return to play in prior investigations, likely partly explaining our relatively lower proportions of return to play. In this
group of 36 patients, ISS was not correlated with return to
same level of play or within 1 Tegner level of play (Tables
3 and 4). However, subgroup analysis of 20 high-level athletes (preinjury Tegner level ≥7) demonstrated that ankle
strength was indeed important and did correlate with return
to prior level of play. We found that for every 16-point
increase in the ISS, patients had an 8.3 times higher rate of
return to the same level of play (P = .055) and a 6.3 times

higher rate of return to within 1 Tegner activity level (P =
.043). Similarly, of the 20 high-level athletes, those that
were able to return to within 1 Tegner level of play were
stronger (mean ISS 83.4, n = 7) compared with those that
were unable to return to within 1 level of play (mean ISS
67.7, n = 13) (P = .018). On the contrary, recreational athletes and low-demand patients (preinjury Tegner level <7)
were able to return to within 1 level of play despite continued strength deficits with a mean ISS of 66.8, n = 14. As
such, in this low-level activity subgroup, there was no statistically significant relationship between strength and
return to play. These results suggest that patients with more
strenuous athletic demands are more dependent on recovery
of ankle strength in the postoperative time period in order to
return to their previous high level of play, whereas regaining strength may be less important for returning to normal
activities for less active patients. The lack of any statistically significant association between ISS and return to play
in subgroups based on age suggests that the level of athletic
demand, rather than age, is the more important consideration in determining whether strength recovery is predictive
of return to play.
Several studies have examined ankle dorsiflexion and
plantarflexion strength following Achilles tendon rupture.
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