Intratendinous Normal Saline Injection of Quadriceps and Patellar Tendon Allografts Does Not Reduce Mechanical Strength at Time Zero

Purpose

To evaluate the tensile strength of human cadaveric quadriceps tendon (QT) and bone–patellar tendon–bone (BTB) allografts augmented by intratendinous saline injection.

Methods

Thirty-three QT and 14 BTB allografts harvested from fresh-frozen human cadaveric knees were tested using a servohydraulic test system. One half of all grafts were injected with 2 mL of intratendinous 0.9% saline, acting as a substitute for PRP, whereas the other half were soaked in saline as a control. Tensile testing was then performed and the ultimate load at failure (N) was measured. Statistical analysis, including descriptive, analysis of variance, and post hoc Tukey analysis, was performed. A P value less than.05 was considered significant.

Results

The mean ultimate load at failure was not significantly different for treated QT grafts and control QT grafts (330 ± 179 N vs 291 ± 195 N, P =.94). The mean ultimate load at failure was also not significantly different for treated BTB grafts and control BTB specimens (553 ± 195 N vs 656 ± 242 N, P =.76).

Conclusions

Intratendinous normal saline injection compared with passive normal saline exposure was not associated with any significant differences in ultimate load at failure for quadriceps and patellar tendon allografts at time zero.

Clinical Relevance

Graft rupture is a feared complication of anterior cruciate ligament reconstruction. The current study may provide surgeons with added confidence that intratendinous therapeutic injections of nonviscous substances do not significantly impair the tensile strength of QT and BTB allografts used in ACL reconstruction at time zero.

Platelet-rich plasma (PRP) is an autologous blood product with numerous orthopaedic applications ranging from pain amelioration in osteoarthritis to intraoperative augmentation of orthopaedic procedures intended to improve postoperative recovery. PRP, concentrated bone marrow aspirate (cBMA), and other orthobiologic injections aim to deliver high concentrations of platelet growth factors, cytokines, and bioactive factors to enhance healing. The concept of orthobiologic augmentation for anterior cruciate ligament (ACL) reconstruction has gained popularity in recent years. ^,^,^,^,^,^,^,^,^,^, Some studies suggest that intratendinous injection of orthobiologic substances may accelerate early graft revascularization, maturation, and incorporation. ^,^, The potential benefits of bioaugmentation for anterior cruciate ligament reconstruction (ACLR) coupled with the simplicity of such procedures may explain adoption of graft augmentation by some orthopaedic surgeons. In a 2021 survey-based study on global trends in ACLR among members of the ACL Study Group, Sherman et al reported that 21% of those surveyed used some type of biological augmentation in primary ACLR. With growing acceptance of graft augmentation in ACLR, it is important to identify potential deleterious effects of introducing fluid substances directly into tendinous grafts, particularly when it is used by more than 1 in 5 surgeons.

Tendons possess unique mechanical properties that make them suitable for use in ligamentous reconstructions, some of which may be disrupted by graft augmentations. In addition to their tensile strength derived largely from type I collagen, tendons are highly viscoelastic, meaning they resist sudden stretching but gradually deform with sustained force. Viscoelasticity is thought to be influenced by collagen orientation and complex interactions between collagenous proteins, water, and proteoglycans. ^, It may be reasonable to hypothesize that any disruptive factors to tendon microarchitecture or the interactions between collagen and proteoglycans, such as an intratendinous fluid injection, may affect tendon viscoelasticity and the ability to resist deforming forces immediately after treatment.

Therefore, the purpose of this study was to evaluate the tensile strength of human cadaveric quadriceps tendon (QT) and bone–patellar tendon–bone (BTB) allografts augmented by intratendinous saline injection. Our null hypothesis was that there would be no difference in tensile strength between specimens treated with intratendinous injection and control at time zero.

Methods

Specimen Preparation

In total, 10 cadaveric donors were used as sources for the grafts in the current study. Demographic data (age and sex) were available for 7 donors, of whom 4 were male. The mean age of cadaveric donors with available age data was 80.4 years. Specimens were obtained from the Maryland State Anatomy Board and were immediately packaged in double-thickness plastic bags and stored at −20°C. All specimens were recovered and frozen within 24 hours postmortem. Specimen preparation included harvest of 2 types of allogenic tendinous grafts: QT and BTB grafts (10 mm in diameter). Grafts were harvested by a single author (E.A.J.) using a similar technique to that described by Staubli et al. ^, A single BTB graft and 2 QT grafts were harvested from the extensor mechanism of each cadaveric specimen. Specimens with subjective irregularities, signs of damage or surgery, and abnormal consistency identified on gross inspection by a single author (E.A.J.) with validation from a second author (K.P.Z.) were excluded.

Treatment Protocol

Among QT and BTB groups, one half the specimens were treated with intratendinous injection and half were soaked in 0.9% normal saline (NS) for 3 minutes as control. Injection treatment was performed by injecting 2 mL of NS midsubstance into the graft using an 18-gauge needle. The volume of NS was chosen to conservatively reflect injection volumes in clinical practice, because there are no clear guidelines or agreement in the existing literature regarding optimal volume for intratendinous augmentation. A single needle entry was made to minimize mechanical trauma to the specimen from the needle and to standardize the protocol for all specimens in that group.

Biomechanical Testing

Specimens were immediately suspended at treatment time zero for tensile strength testing using a servohydraulic testing system with measurements acquired by the system software (Bionix; MTS Systems Corporation, Eden Prairie, MN) ( Fig 1 ). Serrated clamps were fixed to each of the QT grafts and tightened with a torque wrench, consistent with previous validated testing techniques ( Fig 2 ). For BTB grafts, the bone blocks were clamped directly to the tensile testing system. Samples were preloaded to 10 N, then cyclically loaded at 0.5 Hz for 100 cycles between 50 and 200 N as described previously by Yanke et al. Tensile tests were then performed using a 10-mm/min crosshead speed until graft failure, which is a standard, validated test protocol. The maximum load at failure (N) was automatically measured during tensile testing and stress-strain plots were generated by the testing software.

Image, AltText currently not available — Fig 1

Statistical Analysis

The ultimate load at failure was obtained for each specimen. Descriptive statistics consisted of mean and standard deviation. Two-way analysis of variance with post hoc Tukey analysis was used for comparative analysis to evaluate statistical significance. A P value less than 0.05 was considered significant. Statistical analysis was performed in RStudio using the statistical programming language R.

Results

Included Specimens

A total of 57 fresh cadaveric tendon grafts were used in the current investigation, including 14 BTB grafts and 33 QT grafts. Details of cadaveric donors and biomechanical testing results by cadaveric specimen are included in Table 1 . Four QT specimens and 5 BTB specimens were rejected before mechanical testing because of poor tendon quality, poor bone quality or retained material from previous total knee arthroplasty. One treated QT specimen was excluded from analysis after testing because of failure of clamp fixation.

Table 1

Details of Cadaveric Donors and Specimens

Cadaveric Donor	Age, yr	Sex	Specimen Laterality	Graft	Treatment	Reason for Exclusion (if Applicable)	Maximum Force at Failure, N
1	N/A	N/A	Right	QT (1)	Injection		361.11
				QT (2)	Control		54.69
				BTB	Control		692.29
			Left	QT (1)	Injection	Failure of clamp fixation	N/A
				QT (2)	Control		556.04
				BTB	N/A	Previous TKA	N/A
2	N/A	N/A	Right	QT (1)	Injection		433.38
				QT (2)	Control		259.42
				BTB	N/A	Previous TKA	N/A
			Left	QT (1)	Injection		382.93
				QT (2)	Control		416.08
				BTB	N/A	Previous TKA	N/A
3	N/A	N/A	Right	QT (1)	Injection		204.61
				QT (2)	Control		119.59
				BTB	Control		795.43
			Left	QT (1)	Injection		264.72
				QT (2)	Control		258.20
				BTB	Injection		771.95
4	83	M	Right	QT (1)	N/A	Abnormal consistency	N/A
				QT (2)	N/A	Abnormal consistency	N/A
				BTB	Control		643.33
			Left	QT (1)	N/A	Abnormal morphology	N/A
				QT (2)	N/A	Abnormal morphology	N/A
				BTB	Injection		411.32
5	78	M	Right	QT (1)	Injection		325.72
				QT (2)	Control		307.51
				BTB	Control		773.99
			Left	QT (1)	Injection		62.69
				QT (2)	Control		294.81
				BTB	Injection		443.07
6	43	F	Right	QT (1)	Injection		664.90
				QT (2)	Control		495.75
				BTB	N/A	Poor bone quality	N/A
			Left	QT (1)	Injection		256.35
				QT (2)	Control		201.03
				BTB	Injection		585.55
7	86	F	Right	QT (1)	Injection		116.90
				QT (2)	Control		151.26
				BTB	Injection		302.53
			Left	QT (1)	Injection		49.98
				QT (2)	Control		202.62
				BTB	Control		713.86
8	85	F	Right	QT (1)	Injection		428.59
				QT (2)	Control		278.06
				BTB	Control		129.70
			Left	QT (1)	Injection		457.47
				QT (2)	Control		28.77
				BTB	Injection		511.59
9	98	M	Left	QT (1)	Injection		194.67
				QT (2)	Control		81.15
				BTB	N/A	Previous TKA	N/A
10	90	M	Right	QT (1)	Injection		521.42
				QT (2)	Control		727.59
				BTB	Injection		841.57
			Left	QT (1)	Injection		555.04
				QT (2)	Control		517.96
				BTB	Control		842.71